Noise Reduction in Impedance Measurement Circuits

Abstract

Devices having impedance measurement circuits that allow for flicker noise reduction can be implemented in a variety of applications. Carrier suppression techniques can be implemented to remove noise artifacts associated with the carrier signal from its sidebands, thereby substantially removing the carrier signal. Carrier suppression in an AC impedance measurement circuit can be achieved by sensing the carrier signal of the measurement circuit at a transmit location of the measurement circuit and subtracting a weighted version of the carrier signal at a receive location of the measurement circuit. One or more compensating impedances can be used to allow the carrier signal's sidebands to be received with the carrier signal suppressed relative to the receive location.

Description

[0001] Priority application

[0002] This application claims the benefit of priority to U.S. application serial number 17,088,098, filed on November 3, 2020, which claims the benefit of priority to U.S. provisional application serial number 63 / 032,913, filed on June 1, 2020, which is incorporated herein by reference in its entirety. Technical Field

[0003] This document relates to impedance measurement circuits and, in particular, to the reduction of flicker noise in impedance measurement circuits. Background Art

[0004] Flicker noise is a relatively low-frequency noise whose noise power is inversely proportional to frequency. Flicker noise is also known as 1 / f noise. Dynamic techniques, such as chopping, can shift noise components to higher frequencies. A limitation of chopping is that it may not be possible to chop all significant sources of 1 / f noise. For applications where the signal of interest is low-frequency, shifting the noise to higher frequencies effectively eliminates the 1 / f noise problem. Alternatively, the effects of 1 / f noise can be modeled using integrated circuit designs that include margins to account for this noise. In some applications, manufacturing tolerances may not provide acceptable yields, so unacceptable noise may require increased testing during the manufacturing process. New circuit designs that account for or eliminate 1 / f noise can enhance the ability to achieve higher manufacturing yields for desired circuits while still performing in the desired application. Summary of the Invention

[0005] An apparatus having an impedance measurement circuit that allows for noise reduction can be implemented in a variety of applications. In an alternating current (AC) impedance measurement circuit, gain instabilities in the channel can modulate a carrier signal into useful sidebands of the carrier signal. A carrier suppression technique is implemented that substantially removes the carrier signal, and thus the noise artifacts, from the sidebands. Carrier suppression in an AC impedance measurement circuit can be achieved by sensing the carrier signal of the measurement circuit at its transmit location and subtracting a weighted version of the carrier signal at its receive location.

[0006] For example, in certain embodiments, an impedance measurement device may be provided, disclosing: a transmit port for driving a carrier signal to a sample under test; a receive port for receiving a sideband of the carrier signal in response to modulation of the carrier signal from the sample under test; and a compensating impedance coupled between the transmit port and the receive port such that the sideband of the carrier signal is received with the carrier signal suppressed relative to the receive port.

[0007] In certain embodiments, a method for reducing flicker noise in an impedance measurement circuit may be provided, disclosing: transmitting a carrier signal to a sample under test; and receiving sidebands of the carrier signal in response to modulation of the carrier signal from the sample under test, wherein the carrier signal is suppressed in reception of the sidebands using a compensating impedance coupled between a transmit port and a receive port of the impedance measurement circuit.

[0008] In certain embodiments, an apparatus having an impedance measurement circuit may be provided, disclosing: means for transmitting a carrier signal to a sample under test; means for receiving sidebands of the carrier signal in response to modulation of the carrier signal from the sample under test; and means for suppressing the carrier signal in sideband reception, wherein the means for suppressing the carrier signal is coupled between the means for transmitting the carrier signal and the means for receiving the sidebands of the carrier signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The drawings, which are not necessarily drawn to scale, illustrate generally by way of example and not limitation, various embodiments discussed in the present disclosure.

[0010] Figure 1 A single-ended half-circuit model of an application circuit associated with various embodiments for measuring the impedance of a test sample is shown.

[0011] Figure 2 Shows various embodiments related to Figure 1 The application circuit with added resistors and added driving voltage source.

[0012] Figure 3 Shown according to various embodiments Figure 1 An application circuit in which a capacitor is introduced to allow measurement of the instantaneous channel gain.

[0013] Figure 4A The relationship of an applied carrier signal and expected sidebands in individual respiration measurements according to various embodiments is shown.

[0014] Figure 4B shows that due to noise according to various embodiments Figure 4A The carrier frequency extends to the sidebands.

[0015] Figure 5 An example arrangement of an impedance measurement device for measuring the AC impedance of a measured sample, including a compensation impedance for suppressing a carrier signal, is shown according to various embodiments.

[0016] Figure 6 is a block diagram of an impedance measurement apparatus that provides flicker noise suppression in AC impedance measurements of a sample under test, according to various embodiments.

[0017] Figure 7 is a block diagram of a structure having components that provide flicker noise suppression in AC impedance measurements of a sample coupled to the structure, according to various embodiments.

[0018] Figure 8 is a flow chart of features of an example method of reducing flicker noise in an impedance measurement circuit according to various embodiments. DETAILED DESCRIPTION

[0019] The following provides a discussion of example embodiments of an impedance measurement device having components for addressing noise in a measurement signal according to the teachings herein.

[0020] In measurement devices where the purpose of the measurement is to sense parameters with low frequencies, 1 / f noise can cause unacceptable errors in the measurement. Consider individual respiration measurements. In respiration measurements, electrodes are used to measure the impedance of an individual's chest to detect respiration rate. An AC carrier signal, for example, with a representative frequency of 50 kHz, can be applied to the electrodes. The typical impedance of an individual's chest is approximately 2 kΩ. As the individual breathes, the chest impedance is modulated, providing a respiration signal that is approximately 1 ohm modulated by the 2 kΩ chest impedance. Apnea, defined as a sudden cessation of breathing for 10 seconds or longer, can be monitored using respiration measurements. It is desirable not to miss catastrophic apnea events or falsely detect them. Respiratory cessation is indicated if the signal within the respiratory frequency band does not change significantly over 10 seconds. The respiratory rate is typically 0.3 Hz. If the noise in the measurement circuitry exceeds 20 mOs (RMS), the measurement may result in the patient being deemed to be breathing, while an alarm that should have been issued may not have been sounded. For such measurements, flicker noise should be significantly reduced or eliminated.

[0021] In AC impedance measurements where the impedance is modulated, such as in respiration measurements, the data of interest is in the sidebands of the AC signal applied to measure the impedance. However, gain instabilities in the channel of the AC impedance measurement circuit can modulate the carrier signal into the useful sidebands of the carrier signal, resulting in 1 / f noise in low-frequency measurements. Because the useful information about the modulated impedance is in the sidebands, removing the carrier signal at the sensing location is acceptable. Carrier suppression can be implemented, essentially removing the carrier signal and thus the noise artifacts from the sidebands. This carrier suppression can be achieved by sensing the carrier signal at the transmit location of the measurement circuit and subtracting a weighted version of the carrier signal at the receive location of the measurement circuit.

[0022] Figure 1A single-ended half-circuit model of an application circuit for measuring the impedance of a test sample 150 is described. This application circuit model is suitable for 50kHz respiration measurement of an individual where the test sample 150 is a real body, i.e., the resistance 150 is the resistance of a real body. Respiration measurement is a process in which a person's respiratory rate is measured, typically by counting the number of breaths per minute, thereby determining the number of chest rises. The movement of the chest can cause an adjustment in resistance relative to the individual's real body resistance. In a non-limiting example, the model includes an AC drive voltage source 110 that can generate a carrier signal in the form of a 50kHz sine wave. The test sample 150 (which can be a real object) can have a direct current (DC) resistance of 75W. The drive voltage source 110 can be coupled to an electrode connected to the test sample 150 via a capacitor 131 and a drive resistor 132. The capacitor 131 can have a value of 1nF, and the drive resistor 132 can have a resistance value of 25kΩ. The electrode can have an impedance given by an electrode resistor 142 of 900W in parallel with an electrode capacitor 141 having a capacitance of 1nF. The measurement may be sensed at a sense node 109 coupled to the node where the drive resistor 132 is coupled to the electrode, through a 50kW sense resistor 139 in series with a capacitor 138 having a capacitance of 1 nF.

[0023] The electrode impedances are primarily in phase. Not shown in this figure, the individual's breathing modulates the body and electrode impedances, typically modulating by about 1W out of a 1kW combined impedance of electrodes and body.

[0024] There may be excess noise associated with the measurement of the test sample 150 and the modulation of the test sample 150 from the driving voltage source 110. The excess noise can be modeled as gain instability. In various embodiments, the excess noise can be modeled as an instability in the channel gain. For example, under worst-case die conditions, this instability can be on the order of 50 ppm and can have a staircase-like random telegraph signal (RTS) behavior. Although this noise is recorded in hiW variability, this hiW variability can be adjusted by changing the impedance between the sensing nodes ( Figure 1 is an application of analog half-circuits). With this modulation, a variety of methods can be implemented to minimize noise. In one approach, a known impedance can be introduced between the sensing nodes, and the resulting change in noise can be used to determine the noise. Alternatively, since this is a differential system, a negative impedance can be synthesized between the sensing nodes to cancel out some of the noise. Positive and negative impedance refer to categorizing how energy is handled. Positive impedance refers to consuming energy, while negative impedance refers to generating energy. Positive impedance refers to normal impedance, while negative impedance refers to the opposite or opposite impedance. For example, negative impedance can represent the opposite of an increasing voltage, while positive impedance can represent the opposite of a decreasing voltage.

[0025] Figure 2Shows Figure 1 , wherein a resistor 216 and a drive voltage source 217 are added. In operation, the added resistor 216 can pull the sense node 109 toward the negative drive voltage source 217. The negative drive voltage source 217 is coupled to the node 207, which is coupled to the test sample 150 and to the added resistor 216 used as a cancellation resistor. The added resistor 216 has a resistance value of R_Cancel. Figure 1 For the example component values ​​in the example, R_Cancel can be 1.37 MW. Optimally, R_Cancel can be adjusted to precisely (in phase) cancel the carrier content at the sensing node 109 to minimize noise. As a rule of thumb, cancellation can be achieved when the following parameters are achieved:

[0026] R_Cancel / R_Sense=R_Drive / R_Body

[0027] Where R_Body is the combination of the impedance of the electrode (electrode resistor 142 in parallel with electrode capacitor 141) and the real body (e.g., resistor 150). R_Sense is the value of the sense resistor 139, and R_Drive is the resistance value of the drive resistor 132. R_Cancel is used to cancel the carrier at the sense node 109 from the modulation of the test sample 150, but not the sidebands, which have the breathing information of the test sample 150 as a real body. The breathing signal can be attenuated by a small factor of approximately R_Cancel / (R_Cancel+R_Sense), for Figure 2 For component values ​​of circuit elements, this factor should be less than 0.5dB.

[0028] The added resistor 216 with the value of R_Cancel can be implemented as an on-chip resistor digital-to-analog converter (RDAC) without affecting the pin output. For balance in the differential circuit, positive and negative RDACS with a resistance value of R_Cancel can be implemented, where the negative RDACS represents the RDAC on the negative side of the differential circuit. The RDAC can only cancel the in-phase component of the carrier from the driving source 110. If the quadrature component of the waveform at the sensing node 109 is too large, a capacitive digital-to-analog converter (CAPDAC) can be used in a position similar to the RDAC to minimize it. The use of RDAC and CAPDAC is not mutually exclusive. In some cases, both RDAC and CAPDAC can be used to cancel the in-phase and quadrature components of the carrier signal.

[0029] Figure 3 Shows Figure 1The application circuit of FIG. 1 is a circuit diagram of a respiration measurement circuit, wherein capacitor 328 is introduced to allow measurement of the instantaneous channel gain. Using the application circuit portion of the respiration measurement, this allows measurement of the instantaneous channel gain separated from the respiration signal. Capacitor 328 can be implemented as a calibration capacitor (C_Cal). Figure 1 In the example component values ​​of the above example, the value of capacitor 328 can be 2pF. Capacitor 328 is coupled between node 306 to which AC drive source 110 is coupled and sense node 109. According to the model regarding noise, gain error affects both in-phase and quadrature measurements in equal proportions. Figure 1 At the example frequencies, where the body and electrodes are primarily resistive, the effect on the in-phase measurement should be greater than the effect on the quadrature measurement. At the same time, both in-phase and quadrature measurements can separate the respiration signal from the noise. Because the in-phase and quadrature transfer functions of respiration and noise to the sensing node are different, classic noise cancellation strategies can be used to separate the noise from the respiration signal.

[0030] Figure 4A 1 shows the relationship between an applied carrier signal and the expected sidebands in an individual's respiration measurement. The sidebands 401-1 and 401-2 of the carrier signal are generated due to the adjustment of the individual's respiratory activity (e.g., the individual's breathing) to the resistance of the individual's body. In this example, a 55kHz carrier signal is applied, and the sidebands of the respiration are -66dBc, which is offset from the carrier signal by 0.3Hz. These sidebands 401-1 and 401-2 provide information for the respiration measurement. However, noise associated with the carrier signal (e.g., flicker noise) can effectively spread the carrier frequency into the sidebands 401-1 and 401-2, as shown in FIG. Figure 4B As shown in the figure, in the case of gain instability caused by flicker noise, the carrier signal driving the channel to the individual's body generates a carrier extension 403 to the respiratory frequency band as sidebands 401-1 and 401-2, which may cause errors in respiration measurement. To remove the noise associated with the carrier signal, the carrier signal and its noise can be suppressed at the sensing node of the impedance measurement device used for individual respiration measurement.

[0031] Figure 5An embodiment of an exemplary arrangement of an impedance measurement device for measuring the AC impedance of a test sample 550 is shown, the arrangement including compensation impedances 516-1 and 516-2 for suppressing a carrier signal. In some applications, the test sample 550 may be the impedance of an individual's body, such as the chest impedance. Transmit ports 506 and 507 are used to drive a carrier signal along an excitation path PI to sample 550, wherein the carrier signal is an AC signal. Receive ports 508 and 509 are used to receive sidebands of the carrier signal in response to modulation of the carrier signal from the test sample 550, wherein receive ports 508 and 509 are coupled to path P2, which provides a sensing path. The impedance of the test sample 550 may include electrodes providing a connection to path PI. The impedance of the electrodes may be a known value, which may be determined during a calibration process or in testing prior to measuring the test sample 550.

[0032] Path P1 may include capacitors 531 and 533 to block the DC component of the AC carrier signal. Path P1 may include resistor 532 in series with capacitor 531, which is coupled to node 502-1 at one end of the sample under test 550, and capacitor 534 in series with capacitor 533. Capacitor 532 is coupled to node 502-2 at the other end of the sample under test 550, the other end of which is coupled to resistor 532. Nodes 502-1 and 502-2 may be part of the electrodes of the sample under test. Path P2 may include capacitors 536 and 538 to block the DC component in this sensing path. Path P2 may include resistor 539 in series with capacitor 538 (coupled to node 502-1 at one end of the sample under test 550) and resistor 537 in series with capacitor 536 (coupled to node 502-2 at the other end of the sample under test 550, opposite the end coupled to resistor 539).

[0033] The AC impedance of the sample under test 550 is associated with a modulation of the static (DC) impedance of the sample under test 550. Since the sample under test 550 is the individual whose respiration is being measured, the individual's respiration can cause a modulation of the individual's static impedance, such as the resistance of the individual's chest. This modulation modulates the carrier signal applied to the individual, and the effects of this modulation can be sensed by measuring respiration from the inputs to receive ports 508 and 509. Information is provided by the sidebands of the carrier signal caused by the impedance modulation of the sample under test 550.

[0034] To remove noise associated with the carrier signal, compensating impedances 516-1 and 516-2 may be implemented to suppress the carrier signal and its noise at the receiving ports 508 and 509 for sensing. Compensating impedances 516-1 and 516-2 may also be referred to as cancellation impedances. AC measurement devices with compensating impedances are not limited to respiration measurements.

[0035] Compensating impedances 516-1 and 516-2 are coupled between transmit ports 506 and 507 and receive ports 508 and 509 such that the sidebands of the carrier signal are received with the carrier signal suppressed at receive ports 508 and 509. Compensating impedances 516-1 and 516-2 can be coupled between transmit ports 506 and 507 and receive ports 508 and 509 such that carrier signal suppression results from a subtraction operation. Impedance 516-1 can be coupled between transmit port 506 and receive port 509, with impedance 516-2 coupled between receive port 508 and transmit port 507.

[0036] Compensating impedances 516-1 and 516-2 can be selected to match the network coupling transmit ports 506 and 507 and receive ports 508 and 509 to the sample under test 550. The network can include capacitors 531, 533, 536, and 538, resistors 532, 534, 537, and 539, and an impedance associated with the sample under test 550. The impedance associated with the sample under test 550 can include the impedance of the connecting electrodes and the impedance of the sample under test. During the matching process, the impedance of the sample under test 550 can be the unmodulated resistance of the sample 550. Compensating impedances 516-1 and 516-2 can be selected so that a first ratio of the compensating impedances 516-2 and 516-1 to a first impedance coupled to receive ports 508 and 509 is approximately equal to a second ratio of a second impedance coupled to transmit ports 506 and 507 to a combination of the electrode impedance and the sample under test 550 and the sample impedance of the sample under test 550. Compensating impedances 516-1 and 516-2 can be programmable impedances.

[0037] As the modulation of the sample under test 550 decreases, the modulation frequency decreases as the frequency difference between the carrier frequency and the sideband decreases. As the modulation frequency becomes very small, the impedance of the sample under test 550 approaches the static impedance of the sample under test 550. The use of sidebands for measurement can be replaced by an impedance measurement device using compensation impedances 516-1 and 516-2, thereby reporting the non-modulated impedance of the sample under test 550, which can be predetermined during the calibration process.

[0038] Figure 6FIG. 6 is a block diagram of an impedance measurement device 600 that provides flicker noise suppression in AC impedance measurements of a sample 650 under test. In various embodiments, sample 650 may be the actual body of an individual undergoing a test, such as a respiration measurement. Impedance measurement device 600 may include a structure 605 having transmit ports 606 and 607 and receive ports 608 and 609 that may be coupled to sample 650. Structure 605 may be implemented as an integrated circuit or as part of an integrated circuit. Transmit ports 606 and 607 are used to drive a carrier signal to sample 650, where the carrier signal is an AC signal. Receive ports 608 and 609 are used to sense the impedance of sample 650, where the sidebands of the carrier signal are sensed in response to modulation of the carrier signal from sample 650. Connection to sample 650 may be achieved via electrodes coupled to different ends of sample 650. One electrode coupled to sample 650 may include electrical characteristics corresponding to resistor 642 and capacitor 641. Another electrode coupled to a different end of sample 650 may include electrical characteristics corresponding to resistor 644 and capacitor 643.

[0039] In various embodiments, the carrier signal driven from transmit ports 606 and 607 includes a DC component that is blocked from exciting sample 650. For example, in respiration measurement, DC excitation of the individual's body is to be avoided. Capacitors 631 and 633 are used to block the DC component of the AC carrier signal from being directed to sample 650. The path between the sample 650 electrode and transmit ports 606 and 607 may include a resistor 632 in series with capacitor 631, which is coupled to one of the sample 650 electrodes at node 602-1, and may include a resistor 634 in series with capacitor 633, which is coupled to the other sample 650 electrode at node 602-2. The path between the sample 650 electrode and receive ports 608 and 609 for sensing may include capacitors 636 and 638 to block DC components in the sensing path. The path between the sample 650 electrode and receive ports 608 and 609 may include a resistor 639 in series with capacitor 638 coupled to node 602-1 and a resistor 637 in series with capacitor 636 coupled to node 602-2. At receive nodes 608 and 608, capacitors to ground may be used.

[0040] The structure 605 may include an AC drive signal source 610 that can generate a carrier signal to excite the sample 650. The carrier signal is input to a digital-to-analog converter (DAC) 615 having two outputs, one coupled to the transmit port 606 and the other coupled to the transmit port 607. The DAC 615 may include one or more amplifier components or may be implemented as an amplifier. The structure 605 may also include an analog-to-digital converter (ADC) 620 coupled to receive ports 608 and 609 for sensing an AC impedance measurement of the sample 650. The receive port 609 may optionally be coupled to an input of the ADC 620 via a capacitor 622, and the receive port 608 may optionally be coupled to another input of the ADC 620 via a capacitor 621.

[0041] Excessive noise in the signal stimulus sample 650 may be caused by channel gain instability in the output channel of the DAC 615. This excess noise may appear as flicker noise in the AC impedance measurement of the sample 650. This noise may cause the carrier signal to spread, causing errors in the sideband recovery of the carrier signal modulated by the sample 650. This spreading is similar to Figure 4B To recover the desired sidebands that provide information about the AC impedance of sample 650 , the carrier signal and its associated noise may be suppressed for ADC 620 operation.

[0042] To remove noise associated with the carrier signal, compensating impedances 616-1 and 616-2 can be implemented to suppress the carrier signal and its noise at receive ports 608 and 609 for sensing. Compensating impedances 616-1 and 616-2 can also be referred to as cancellation impedances. Compensating impedances 616-1 and 616-2 are coupled to receive ports 609 and 608, respectively.

[0043] Compensating impedances 616-1 and 616-2 can be coupled between transmit ports 606 and 607 and receive ports 608 and 609 so that sidebands of the carrier signal are received with the carrier signal suppressed relative to receive ports 608 and 609. Compensating impedances 616-1 and 616-2 can be coupled between transmit ports 606 and 607 and receive ports 608 and 609 so that carrier signal suppression results from a subtraction operation. Impedance 616-1 can be coupled between transmit port 606 and receive port 609, while impedance 616-2 can be coupled between receive port 608 and transmit port 607. Compensating impedances 616-1 and 616-2 can be selected to match the network coupling transmit ports 606 and 607 and receive ports 608 and 609 to sample 650. The network can include capacitors 631, 633, 636, and 638, resistors 632, 634, 637, and 639, and an impedance associated with sample 650. The impedance associated with sample 650 may include the impedance of the connecting electrodes and the impedance of sample 650. During the matching process, the resistance of sample 650 may be the unmodulated resistance of sample 650. Compensation impedances 616-1 and 616-2 may be selected so that a first ratio of compensation impedances 616-1 and 616-2 to a first impedance coupled to receive ports 608 and 609 is approximately equal to a second ratio of a second impedance coupled to transmit ports 606 and 607 to a combination of the electrode impedance and the sample under test 650 and the sample impedance of the sample under test 650. Compensation impedances 616-1 and 616-2 may be programmable impedances.

[0044] The two outputs of DAC 615, coupled to transmit ports 606 and 607, can provide a carrier signal as a differential signal. One of the two outputs is coupled to transmit port 606, which is arranged as a positive drive node, and the other is coupled to transmit port 607, which is arranged as a negative drive node. The two inputs of ADC 620 can be coupled to receive ports 609 and 608. One of the two inputs is coupled to receive port 608, which is arranged as a positive sense node, and the other is coupled to receive port 609, which is arranged as a negative sense node. Compensation impedance 616-1 is coupled between positive drive node 606 and negative sense node 609. Compensation impedance 616-2 is coupled between negative drive node 607 and positive sense node 608. This arrangement of positive and negative nodes can provide compensation impedances 616-1 and 616-2 to effectively suppress the carrier signal from the subtraction operation. In other embodiments, ADC 620 can be configured as a single-ended arrangement, and compensation impedance 616-1 can be omitted.

[0045] The structure 605 may include a mixer 625. The mixer 625 mixes the carrier signal from the AC drive signal source 610 with the output of the ADC 620. The mixer 625 may provide two outputs: an in-phase signal I and a quadrature-phase signal Q. The structure 605 may include other components that operate on the signals I and Q to analyze the sensed signal to make one or more impedance measurements of the sample 650. Alternatively, the signals I and Q may be provided to a structure separate from the structure 605, for example, to a different die than the die on which the structure 605 resides.

[0046] Figure 7 is a block diagram of a structure 705 having components for providing flicker noise suppression in an AC impedance measurement of a sample coupled to the structure 705. The flicker noise suppression may be achieved by suppressing a carrier signal received from the sample that is detected by a carrier signal driven from the structure 705 to the sample. The structure 705 may include components that are similar in design or operation to the structure 705. Figure 6 Components similar to those of structure 605 of FIG. Structure 705 may include transmit ports 706 and 707 and receive ports 708 and 709, which may be coupled to a sample under test. In various embodiments, the sample under test that may be measured using structure 705 may be the actual body of an individual undergoing a test such as a respiration measurement. Structure 705 may be implemented as an integrated circuit or as part of an integrated circuit. Transmit ports 706 and 707 are used to drive a carrier signal to the sample under test, where the carrier signal is an AC signal. Receive ports 708 and 709 are used to sense the impedance of the sample under test, where the sidebands of the carrier signal are sensed in response to the modulation of the carrier signal by the sample.

[0047] The structure 705 may include an AC drive signal source 710 that can generate a carrier signal to excite the sample under test. The carrier signal is input to a DAC 715 having two outputs, one coupled to a transmit port 706 and the other coupled to a transmit port 707. The DAC 715 may include one or more amplifier components, or may be implemented as an amplifier. The structure 705 may also include an ADC 720 coupled to receive ports 708 and 709 for sensing an AC impedance measurement of the sample under test. The receive port 709 may optionally be coupled to an input of the ADC 720 via a capacitor 722, and the receive port 708 may optionally be coupled to another input of the ADC 720 via a capacitor 721.

[0048] Excessive noise in the signal stimulating the sample under test may be caused by channel gain instability in the output channel of DAC 715. This excessive noise can appear as flicker noise in the AC impedance measurement of the sample. This noise can cause the carrier signal to spread, causing the sideband recovery of the carrier signal modulated by the sample to be affected by errors. This spreading is similar to Figure 4BIn order to recover the desired sidebands that provide information about the AC impedance of the sample being measured, the operation of the carrier signal and its associated noise may be suppressed by the ADC 720 .

[0049] To remove noise associated with the carrier signal, compensating impedances 716-1 and 716-2 can be implemented to suppress the carrier signal and its noise at receive ports 708 and 709 for sensing. Compensating impedances 716-1 and 716-2 can also be referred to as cancellation impedances. Compensating impedances 716-1 and 716-2 are coupled to receive ports 709 and 708, respectively.

[0050] Compensating impedances 716-1 and 716-2 can be coupled between transmit ports 706 and 707 and receive ports 708 and 709 such that sidebands of the carrier signal are received with the carrier signal suppressed relative to receive ports 708 and 709. Compensating impedances 716-1 and 716-2 can be coupled between transmit ports 706 and 707 and receive ports 708 and 709 such that carrier signal suppression results from a subtraction operation. Impedance 716-1 can be coupled between transmit port 706 and receive port 709, with impedance 716-2 coupled between receive port 708 and transmit port 707.

[0051] Compensating impedances 716-1 and 716-2 can be selected to match the network coupling transmit ports 706 and 707 and receive ports 708 and 709 to the sample under test. The network to which structure 705 can be coupled can include impedances, impedances associated with the sample, and impedances connecting electrodes to the sample. During the matching process, the impedance of the sample under test can be the unmodulated resistance of the sample. Compensating impedances 716-1 and 716-2 can be selected such that a first ratio of the compensating impedances 716-1 and 716-2 to a first set of impedances of the network coupled to receive ports 708 and 709 is approximately equal to a second ratio of a second set of impedances coupled to transmit ports 706 and 707 to a combination of the electrode impedances and the sample under test and the sample impedance of the sample under test. Compensating impedances 716-1 and 716-2 can be programmable impedances.

[0052] The two outputs of DAC 715, coupled to transmit ports 706 and 707, can provide a carrier signal as a differential signal, with one of the two outputs coupled to transmit port 706, arranged as a positive drive node, and the other of the two outputs coupled to transmit port 707, arranged as a negative drive node. Two inputs of ADC 720, coupled to receive ports 709 and 708, can be provided, with one of the two inputs coupled to receive port 708, arranged as a positive sense node, and the other of the two inputs coupled to receive port 709, arranged as a negative sense node. Compensation impedance 716-1 is coupled between positive drive node 706 and negative sense node 709. Compensation impedance 716-2 is coupled between negative drive node 707 and positive sense node 708. This arrangement of positive and negative nodes can provide compensation impedances 716-1 and 716-2 to effectively suppress the carrier signal from the subtraction operation. In other embodiments, ADC 720 can be configured as a single-ended arrangement, and compensation impedance 716-1 can be omitted.

[0053] The structure 705 may include a mixer 725. The mixer 725 mixes the carrier signal from the AC drive signal source 710 with the output of the ADC 720. The mixer 725 may provide two outputs: an in-phase signal I and a quadrature-phase signal Q, which are generated by mixing the carrier signal with the output of the ADC 720 coupled to the receive ports 708 and 709. The structure 705 may include other components that operate on the signals I and Q to analyze the sensed signals to perform one or more impedance measurements on the sample under test. Alternatively, the signals I and Q may be provided to a structure separate from the structure 705, for example, to a die different from the die on which the structure 705 is located.

[0054] The structure 705 may include a processing device 730 and a memory 735 coupled to the processing device 730. The memory 735 is a machine-readable storage device that stores instructions that, when executed by the processing device 730, cause operations to be performed. The processing device 730 may be implemented as one or more processors, such as, but not limited to, one or more digital signal processors (DSPs). The processing device 730 may perform a plurality of operations related to AC impedance measurement of a sample coupled to the structure 705. The operations performed by the processing device 730 may include operations on I and Q signals from the mixer 725. The operations performed by the processing device 730 include controlling compensation impedances 716-1 and 716-2 configured as programmable impedances. The processing device 730 may perform operations to iteratively adjust the compensation impedances 716-1 or 716-2 to substantially minimize the carrier signal observed at the receive ports 708 and 709. The processing device 730 may perform operations to adjust the compensation impedances 716-1 and 716-2 so that a first ratio of the compensation impedances 716-1 and 716-2 to a first impedance coupled to the receive ports 708 and 709 is approximately equal to a second ratio of a second impedance coupled to the transmit ports 706 and 707 to a combination of the electrode impedance and the measured sample and sample impedance.

[0055] The processing device 730 can perform operations to adjust the compensating impedance 716-1 or 716-2 by adjusting the programmable resistance and programmable capacitance of the corresponding compensating impedance 716-1 or 716-2. The programmable resistance of the compensating impedance 716-1 or 716-2 can be implemented in many conventional arrangements that can be implemented in an integrated circuit. The programmable capacitance of the compensating impedance 716-1 or 716-2 can be implemented in many conventional arrangements that can be implemented in an integrated circuit. The processing device 730 can perform operations to generate an impedance value of the measured sample in a non-modulated state based on the impedance information about the compensating impedance 716-1 or 716-2.

[0056] Processing device 730 may perform operations to add estimated values ​​of one or more of compensation impedance 716-1, compensation impedance 716-2, and a combination of compensation impedances 716-1 and 716-2 to the I and Q signals output by processing device 730 from mixer 725. Processing device 730 may be arranged to control mixer 725 and ADC 720. In another approach, the estimated values ​​may be added by processing device 730 to the inputs of mixer 725 along with the signal from the output of ADC 720. The effect of adding the estimated values ​​to the I and Q signals is to reconstruct the output that would occur without carrier cancellation and without noise. This can avoid the need for an additional output path from the device to transmit the estimate, thereby simplifying the implementation of carrier cancellation. If the compensating impedance serving as the canceling impedance is a capacitor, its value may be added to the Q signal after mixer 725. If the compensating impedance is a resistor, its value may be added to the I signal after mixer 725.

[0057] In various embodiments, an impedance measurement device may include: a transmit port for driving a carrier signal to a sample under test; a receive port for receiving a sideband of the carrier signal in response to modulation of the carrier signal from the sample under test; and a compensation impedance coupled between the transmit port and the receive port such that the sideband of the carrier signal is received with the carrier signal suppressed relative to the receive port. The impedance measurement device may include a second transmit port, a second receive port, and a second compensation impedance, wherein the second compensation port is arranged together with the compensation impedance, the transmit port, and the receive port such that the carrier signal suppression is generated by a subtraction operation.

[0058] This impedance measurement device, or variations of similar impedance measurement devices, can include multiple different embodiments, which can be combined depending on the application of the impedance measurement device or the architecture of the system implementing the impedance measurement device. This impedance measurement device can include: a transmit port being one of two transmit ports, a receive port being one of two receive ports, a compensation impedance being one of the two compensation impedances, a digital-to-analog converter, and an analog-to-digital converter. The digital-to-analog converter can have two outputs coupled to the two transmit ports to provide a carrier signal as a differential signal, one of the two outputs coupled to one of the two transmit ports arranged as a positive drive node, and the other of the two outputs coupled to the other of the two transmit ports arranged as a negative drive node. The analog-to-digital converter can have two inputs coupled to the two receive ports, one of the two inputs coupled to one of the two receive ports arranged as a positive sense node, and the other of the two inputs coupled to the other of the two receive ports arranged as a negative sense node. A first of the two compensation impedances can be coupled between the positive drive node and the negative sense node, and a second of the two compensation impedances can be coupled between the negative drive node and the positive sense node.

[0059] Variations of this impedance measurement device, or similar impedance measurement devices, may include a compensating impedance matched to a network coupling a transmit port and a receive port to a sample under test, the network including the sample under test. The compensating impedance may be selected such that a first ratio of the compensating impedance to a first impedance coupled to the receive port is approximately equal to a second ratio of a second impedance coupled to the transmit port to a combination of an electrode impedance and the sample under test and the sample impedance. Variations may include the compensating impedance being a programmable impedance under the control of a processing device, wherein the processing device is operable to iteratively adjust the compensating impedance to minimize a carrier signal relative to the receive port. This iterative adjustment of the compensating impedance may be used to generate an impedance value of the sample under test in a non-modulated state based on impedance information about the compensating impedance.

[0060] Such an impedance measurement device, or variations of similar impedance measurement devices, may include an analog-to-digital converter coupled to the receive port; a mixer for mixing the carrier signal and an output of the analog-to-digital converter to produce an in-phase signal and a quadrature-phase signal; and a processing device operable to selectively add an estimate of the compensation impedance to the in-phase signal or the quadrature-phase signal output from the mixer.

[0061] A processing device integrated into or networked with the impedance measurement device may operate on the in-phase signal and the quadrature-phase signal to generate information about the sample being measured.

[0062] A device having an impedance measurement circuit may include: means for transmitting a carrier signal to a sample under test; means for receiving sidebands of the carrier signal in response to modulation of the carrier signal from the sample under test; and means for suppressing the carrier signal during sideband reception, wherein the means for suppressing the carrier signal is coupled between the means for transmitting the carrier signal and the means for receiving the sidebands of the carrier signal. The means for transmitting the carrier signal may include: a positive drive node for transmitting a positive drive signal to a first electrode coupled to the sample under test; and a negative drive node for transmitting a negative drive signal to a second electrode coupled to the sample under test opposite to the coupling of the first electrode to the sample under test. The means for suppressing the carrier signal may include: a first compensation impedance coupled between the positive drive node and a negative sense node of the means for receiving the sidebands of the carrier signal; and a second compensation impedance coupled between the negative drive node and the positive sense node of the means for receiving the sidebands of the carrier signal.

[0063] Variations of such an apparatus with an impedance measurement circuit or a similar apparatus with an impedance measurement circuit may include a plurality of different embodiments, which may be combined depending on the application of the apparatus with an impedance measurement circuit or the architecture of the system in which the apparatus with an impedance measurement circuit is implemented. The apparatus with an impedance measurement circuit may include means for suppressing a carrier signal, including means for adjusting the means for suppressing the carrier signal. The apparatus with an impedance measurement circuit may include means for mixing the carrier signal with a received sideband version of the carrier signal and means for processing information. The means for processing information may include means for generating an impedance value of a sample under test in a non-modulated state from impedance information about the means for suppressing the carrier signal, and combining the impedance value of the sample under test in the non-modulated state with the measured impedance of the sample under test from the received sideband.

[0064] Figure 8 This is a flow chart featuring an embodiment of an example method 800 for reducing flicker noise in an impedance measurement circuit. At 810, a carrier signal is transmitted to a sample under test. At 820, sidebands of the carrier signal are received in response to modulation of the carrier signal from the sample under test. At 830, the carrier signal is suppressed during reception of the sidebands using a compensating impedance coupled between a transmit port and a receive port of the impedance measurement circuit. Suppression of the carrier signal can be achieved using a subtraction operation.

[0065] Method 800 or variations of methods similar to method 800 may include multiple different embodiments that can be combined depending on the application of the methods and / or the architecture of the system implementing the methods. Such a method may include sending a carrier signal to include sending a positive drive signal to a first electrode coupled to the sample under test and sending a negative drive signal to a second electrode coupled to the sample under test opposite to the coupling of the first electrode to the sample under test. A first compensating impedance of the compensating impedance may be coupled between a positive drive node of a transmitting port and a negative sense node of a receiving port. In this structure, a second compensating impedance of the compensating impedance may be coupled between the negative drive node of the transmitting port and the positive sense node of the receiving port.

[0066] Method 800 or variations of methods similar to method 800 may include adjusting the compensation impedance such that a first ratio of the compensation impedance to a first impedance coupled to the receive port is approximately equal to a second ratio of a second impedance coupled to the transmit port to a combination of the electrode impedance and the measured sample and sample impedance. Method 800 or variations of methods similar to method 800 may include adjusting the compensation impedance by adjusting a programmable resistor and a programmable capacitor under the control of a processing device. Furthermore, adjusting the compensation impedance may include iteratively adjusting the compensation impedance to minimize a carrier signal at the receive port of the impedance measurement circuit. The programmable resistor and programmable capacitor may be implemented in various ways. For example, the programmable resistor may be implemented as a plurality of resistors each connected in series in parallel with a switch under the control of a processing device to selectively bypass the individual resistors. The programmable capacitor may be implemented as a group of capacitors having a common node, each capacitor connected in series with a switch coupled to the common node of all switches associated with the group of capacitors, wherein each switch is under the control of the processing device. Other forms of programmable resistors and programmable capacitors may also be used.

[0067] Variations of method 800 or methods similar to method 800 may include mixing the carrier signal with a version of the carrier signal having received sidebands suppressed; outputting an in-phase signal and a quadrature-phase signal; and processing the in-phase signal.

[0068] The following are example embodiments of devices having impedance measurement circuits and related methods according to the teachings herein.

[0069] An example impedance measurement device 1 may include: a transmit port for driving a carrier signal to a sample under test; a receive port for receiving a sideband of the carrier signal in response to modulation of the carrier signal from the sample under test; and a compensating impedance coupled between the transmit port and the receive port such that the sideband of the carrier signal is received with the carrier signal suppressed relative to the receive port.

[0070] An example impedance measurement device 2 may include features of the example impedance measurement device 1 and may include: the impedance measurement device includes a second transmit port, a second receive port, and a second compensation impedance, the second compensation port being arranged together with the compensation impedance, the transmit port, and the receive port such that the carrier signal suppression results from a subtraction operation.

[0071] The example impedance measurement device 3 may include features of any of the aforementioned example impedance measurement devices and may include: the impedance measurement device includes: the transmit port is one of two transmit ports, the receive port is one of two receive ports, and the compensation impedance is one of two compensation impedances; a digital-to-analog converter having two outputs coupled to the two transmit ports to provide the carrier signal as a differential signal, one of the two outputs coupled to one of the two transmit ports arranged as a positive drive node, and the other of the two outputs coupled to the other of the two transmit ports arranged as a negative drive node; an analog-to-digital converter having two inputs coupled to the two receive ports, one of the two inputs coupled to one of the two receive ports arranged as a positive sense node, and the other of the two inputs coupled to the other of the two receive ports arranged as a negative sense node; a first compensation impedance of the two compensation impedances coupled between the positive drive node and the negative sense node; and a second compensation impedance of the two compensation impedances coupled between the negative drive node and the positive sense node.

[0072] The example impedance measurement device 4 may include features of any of the aforementioned example impedance measurement devices and may include the compensating impedance being matched to a network coupling the transmit port and the receive port to the sample under test, the network including the sample under test.

[0073] The example impedance measurement device 5 may include features of any of the aforementioned example impedance measurement devices and may include selecting the compensation impedance so that a first ratio of the compensation impedance to a first impedance coupled to the receive port is approximately equal to a second ratio of a second impedance coupled to the transmit port to a combination of an electrode impedance and the measured sample and sample impedance.

[0074] The example impedance measurement apparatus 6 may include features of any of the aforementioned example impedance measurement apparatuses and may include: the compensation impedance being a programmable impedance under the control of a processing device, wherein the processing device is operable to iteratively adjust the compensation impedance to minimize the carrier signal relative to the receive port.

[0075] The example impedance measurement device 7 may include features of any of the aforementioned example impedance measurement devices and may include: an analog-to-digital converter coupled to the receive port; a mixer for mixing the carrier signal and the output of the analog-to-digital converter to produce an in-phase signal and a quadrature-phase signal; and a processing device operable to selectively add an estimate of the compensation impedance to the in-phase signal or the quadrature-phase signal output from the mixer.

[0076] An example apparatus 8 having an impedance measurement circuit may include: means for transmitting a carrier signal to a sample under test; means for receiving sidebands of the carrier signal in response to modulation of the carrier signal from the sample under test; and means for suppressing the carrier signal in sideband reception, wherein the means for suppressing the carrier signal is coupled between the means for transmitting the carrier signal and the means for receiving the sidebands of the carrier signal.

[0077] Example device 9 with impedance measurement circuitry may include features of example device 8 with impedance measurement circuitry, and may include: a component for sending a carrier signal including: a positive drive node for sending a positive drive signal to a first electrode coupled to the sample under test; and a negative drive node for sending a negative drive signal to a second electrode coupled to the sample under test opposite to the coupling of the first electrode to the sample under test.

[0078] Example device 10 with impedance measurement circuitry may include features of example device 8 or 9 with impedance measurement circuitry, and may include: a component that suppresses a carrier signal including: a first compensating impedance coupled between a positive drive node and a negative sense node of the component that receives a sideband of the carrier signal; and a second compensating impedance coupled between the negative drive node and the positive sense node of the component that receives a sideband of the carrier signal.

[0079] The example apparatus 11 having an impedance measurement circuit may include features of any of the aforementioned example apparatuses having an impedance measurement circuit, and may include that the means for suppressing a carrier signal includes means for adjusting the means for suppressing a carrier signal.

[0080] The example device 12 with impedance measurement circuitry may include features of any of the aforementioned example devices with impedance measurement circuitry, and may include: means for mixing the carrier signal with a version of the received sideband of the carrier signal; means for processing an in-phase signal generated from the means to mix the carrier signal with a version of the received sideband of the carrier; and means for processing information to: generate an impedance value of the sample under test in a non-modulated state from impedance information about the means for suppressing the carrier signal; and combining the impedance value of the sample under test in the non-modulated state with the measured impedance of the sample under test from the received sideband.

[0081] An example method 1 for reducing flicker noise in an impedance measurement circuit may include: transmitting a carrier signal to a sample under test; and receiving sidebands of the carrier signal in response to modulation of the carrier signal from the sample under test, wherein the carrier signal is suppressed in reception of the sidebands using a compensating impedance coupled between a transmit port and a receive port of the impedance measurement circuit.

[0082] Example method 2 for reducing flicker noise in an impedance measurement circuit may include features of example method 1 for reducing flicker noise in an impedance measurement circuit and may include suppressing the carrier signal by using a subtraction operation.

[0083] Example method 3 of reducing flicker noise in an impedance measurement circuit may include features of any of the aforementioned example methods of reducing flicker noise in an impedance measurement circuit, and may include: sending the carrier signal includes sending a positive drive signal to a first electrode coupled to the sample under test, and sending a negative drive signal to a second electrode coupled to the sample under test opposite to the coupling of the first electrode to the sample under test.

[0084] Example method 4 for reducing flicker noise in an impedance measurement circuit may include features of example method 3 for reducing flicker noise in an impedance measurement circuit, features of any of the aforementioned example methods for reducing flicker noise in an impedance measurement circuit, and may include: a first compensation impedance of the compensation impedance is coupled between a positive drive node of a transmitting port and a negative sense node of a receiving port; and a second compensation impedance of the compensation impedance is coupled between the negative drive node of the transmitting port and a positive sense node of the receiving port.

[0085] Example method 5 for reducing flicker noise in an impedance measurement circuit may include features of any of the aforementioned example methods for reducing flicker noise in an impedance measurement circuit, and may include: adjusting the compensation impedance so that a first ratio of the compensation impedance to a first impedance coupled to the receive port is approximately equal to a second ratio of a second impedance coupled to the transmit port to a combination of an electrode impedance and the measured sample and sample impedance.

[0086] Example method 6 for reducing flicker noise in an impedance measurement circuit may include features of any of the aforementioned example methods for reducing flicker noise in an impedance measurement circuit, and may include adjusting the compensation impedance by adjusting a programmable resistor and a programmable capacitor under control of a processing device.

[0087] Example method 7 for reducing flicker noise in an impedance measurement circuit may include features of example method 6 for reducing flicker noise in an impedance measurement circuit, features of any of the aforementioned example methods for reducing flicker noise in an impedance measurement circuit, and may include: adjusting the compensation impedance includes iteratively adjusting the compensation impedance to minimize the carrier signal at the receiving port of the impedance measurement circuit.

[0088] Example method 8 for reducing flicker noise in an impedance measurement circuit may include features of example method 5 for reducing flicker noise in an impedance measurement circuit, features of any of the aforementioned example methods for reducing flicker noise in an impedance measurement circuit, and may include: mixing the carrier signal with a version of the received sideband of the carrier signal in which the carrier signal is suppressed; outputting an in-phase signal and an orthogonal-phase signal; and processing the in-phase signal.

[0089] Example method 9 for reducing flicker noise in an impedance measurement circuit may include features of any of the aforementioned example methods 1-8 for reducing flicker noise in an impedance measurement circuit, and may include performing functions associated with any features of example impedance measurement devices 1-7 and example devices 8-14 having an impedance measurement circuit, as well as any features of the example impedance measurement devices and example devices having impedance measurement circuitry associated with the figures herein.

[0090] The above detailed description refers to the accompanying drawings, which illustrate, by way of illustration and not limitation, various embodiments that may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice these and other embodiments. Other embodiments may be utilized, and structural, logical, mechanical, and electrical changes may be made to these embodiments. The various embodiments are not necessarily mutually exclusive, as some embodiments may be combined with one or more other embodiments to form new embodiments. Therefore, the above detailed description should not be limited thereto.

[0091] Although specific embodiments have been shown and described herein, it will be understood by those skilled in the art that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. Various embodiments utilize permutations and / or combinations of the embodiments described herein. It should be understood that the foregoing description is intended to be illustrative and not restrictive, and that the phraseology or terminology used herein is for descriptive purposes only.

Claims

1. An impedance measuring device, comprising: A transmitting port for driving a carrier signal to a sample under test; a receiving port for receiving a sideband of the carrier signal in response to modulation of the carrier signal from the sample under test; a compensating impedance coupled between the transmit port and the receive port such that the sideband of the carrier signal is received with the carrier signal suppressed relative to the receive port; a mixer for mixing the carrier signal with a received sideband version of the carrier signal; and A processing device configured to: generating an impedance value of the measured sample in a non-modulated state from the impedance information about the compensation impedance; and The impedance value of the measured sample in the non-modulated state is combined with the measured impedance of the measured sample from the received sideband.

2. The impedance measuring device according to claim 1, wherein: The impedance measurement device includes a second transmit port, a second receive port, and a second compensating impedance arranged together with the compensating impedance, the transmit port, and the receive port such that suppression of the carrier signal results from a subtraction operation.

3. The impedance measuring device according to claim 1, wherein: The impedance measuring device comprises: The transmitting port is one of two transmitting ports, the receiving port is one of two receiving ports, and the compensating impedance is one of two compensating impedances; a digital-to-analog converter having two outputs coupled to the two transmit ports to provide the carrier signal as a differential signal, one of the two outputs coupled to one of the two transmit ports arranged as a positive drive node, and the other of the two outputs coupled to one of the two transmit ports arranged as a negative drive node; an analog-to-digital converter having two inputs coupled to the two receiving ports, one of the two inputs coupled to one of the two receiving ports arranged as a positive sensing node, and the other of the two inputs coupled to the other of the two receiving ports arranged as a negative sensing node; a first compensation impedance of the two compensation impedances coupled between the positive drive node and the negative sense node; and A second compensation impedance of the two compensation impedances is coupled between the negative drive node and the positive sense node.

4. The impedance measuring device according to claim 1, wherein: The compensating impedance is matched to a network coupling the transmit port and the receive port to the sample under test, the network including the sample under test.

5. The impedance measuring device according to claim 1, wherein The compensating impedance is selected such that a first ratio of the compensating impedance to a first impedance coupled to the receiving port is equal to a second ratio of a second impedance coupled to the transmitting port to a combination of an electrode impedance and a sample impedance of the measured sample.

6. The impedance measuring device according to claim 1, wherein The compensation impedance is a programmable impedance under the control of a processing device, wherein the processing device is operable to iteratively adjust the compensation impedance to minimize the carrier signal relative to the receive port.

7. The impedance measuring device according to claim 1, wherein The impedance measuring device comprises: an analog-to-digital converter coupled to the receiving port; wherein the mixer is configured to mix the carrier signal and the output of the analog-to-digital converter to generate an in-phase signal and a quadrature-phase signal; and wherein the processing means is operable to selectively add an estimate of the compensation impedance to the in-phase signal or the quadrature-phase signal output from the mixer.

8. A method for reducing flicker noise in an impedance measurement circuit, the method comprising: Sending a carrier signal to the sample under test; receiving a sideband of the carrier signal in response to modulation of the carrier signal from the sample under test; suppressing the carrier signal in reception of the sideband using a compensating impedance coupled between a transmit port and a receive port of the impedance measurement circuit; mixing the carrier signal with a version of the received sideband of the carrier signal; generating an impedance value of the measured sample in a non-modulation state from impedance information about the compensation impedance that suppresses the carrier signal; and The impedance value of the measured sample in the non-modulated state is combined with the measured impedance of the measured sample from the received sideband.

9. The method according to claim 8, wherein The method includes suppressing the carrier signal by using a subtraction operation.

10. The method according to claim 8, wherein Transmitting the carrier signal includes transmitting a positive drive signal to a first electrode coupled to the sample under test, and transmitting a negative drive signal to a second electrode coupled to the sample under test opposite to the coupling of the first electrode to the sample under test.

11. The method according to claim 10, wherein: A first compensation impedance of the compensation impedance is coupled between the positive drive node of the transmit port and the negative sense node of the receive port; and a second compensation impedance of the compensation impedance is coupled between the negative drive node of the transmit port and the positive sense node of the receive port.

12. The method according to claim 8, wherein The method includes adjusting the compensation impedance so that a first ratio of the compensation impedance to a first impedance coupled to the receive port is equal to a second ratio of a second impedance coupled to the transmit port to a combination of an electrode impedance and a sample impedance of the measured sample.

13. The method according to claim 8, wherein The method includes adjusting the compensation impedance by adjusting a programmable resistor and a programmable capacitor under control of a processing device.

14. The method according to claim 13, wherein: Adjusting the compensating impedance includes iteratively adjusting the compensating impedance to minimize the carrier signal at the receiving port of the impedance measurement circuit.

15. The method according to claim 8, wherein the method comprises: Output in-phase signal and quadrature-phase signal; and The in-phase signal is processed.

16. A device having an impedance measurement circuit, the device comprising: A component for sending a carrier signal to a sample under test; means for receiving a sideband of the carrier signal in response to modulation of the carrier signal from the sample under test; and means for suppressing the carrier signal in reception of the sideband, wherein the means for suppressing the carrier signal is coupled between means for transmitting the carrier signal and means for receiving the sideband of the carrier signal; means for mixing the carrier signal with a version of the received sideband of the carrier signal; and Components used to process information to: generating an impedance value of the measured sample in a non-modulation state from impedance information about the means for suppressing the carrier signal; and The impedance value of the measured sample in the non-modulated state is combined with the measured impedance of the measured sample from the received sideband.

17. The device according to claim 16, wherein The component for sending the carrier signal includes: a positive driving node for sending a positive driving signal to a first electrode coupled to the sample under test; and a negative driving node for sending a negative driving signal to a second electrode coupled to the sample under test opposite to the coupling of the first electrode to the sample under test.

18. The device according to claim 17, wherein The means for suppressing the carrier signal comprises: a first compensating impedance coupled between a positive drive node and a negative sense node of the means for receiving a sideband of the carrier signal; and A second compensating impedance is coupled between a negative drive node and a positive sense node of the means for receiving a sideband of the carrier signal.

19. The device according to claim 16, wherein The means for suppressing the carrier signal includes means for adjusting the means for suppressing the carrier signal.

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