Reconfigurable Transconductance Conversion Bias Circuit and Tuning Method Using the Same

Abstract

The present invention discloses a reconfigurable transconductance conversion bias circuit and a tuning method using the circuit, which can achieve gm cell tuning, improve the applicable range of the automatic tuning circuit of the integration structure. The bias circuit includes an amplifier, a gm cell, a capacitor, a switch, a voltage source VDD, a resistor R0, and a current mirror circuit. The gm cell is in the form of a resistor. The current mirror circuit includes a first current mirror circuit and a second current mirror circuit. The voltage source VDD is connected to the positive input terminal and the first current input terminal of the amplifier through the first current mirror circuit respectively. The voltage source VDD is connected to the negative input terminal and the second current input terminal of the amplifier through the second current mirror circuit respectively. The second current mirror circuit is connected to the output terminal of the amplifier through the gm cell. The method includes mirroring currents I1 and I2 to transistors M2 and M9 respectively to perform reconfigurable control on the filter or modulator, and performing feedback tuning on the current of the gm cell through the bias voltage Vb until the bias voltage is stable.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuits, and specifically to a reconfigurable transconductance conversion bias circuit for a tuning circuit and a tuning method using the circuit. Background Art

[0002] During the design process of a circuit system, process variations and temperature changes will both have a certain impact on the circuit performance. The circuit system mainly includes integrators, filters, modulators, etc. The integrator is the basic module of the filter and modulator circuits. Currently, the commonly used integrator structures mainly include active RC (active RC) and transconductance-capacitance (gm-c). Process variations and temperature and other factors will affect the resistors and capacitors in the active RC integrator, or the gm values and capacitance values in the gm-c integrator. The impact is mainly reflected in the deviation of the center frequency and bandwidth. When affected by process variations and temperature and other factors to a large extent, the deviation of the center frequency and bandwidth can reach 50%. Therefore, in the current circuit designs of filters and modulators, etc., appropriate tuning techniques are usually added to reduce the actual deviation through the tuning techniques. The existing tuning circuit techniques for filters or modulators are relatively mature. For example, in a circuit system with low power consumption requirements, a frequency tuning technique based on a phase-locked loop can be used. When the circuit system has high power consumption requirements but low accuracy requirements, an integral structure calibration circuit or a digital frequency tuning technique can be used.

[0003] Currently, the frequency automatic tuning technique for filters or modulators with a gm-c structure is mainly a frequency tuning technique based on a phase-locked loop. This technique has the advantage of high accuracy, but has the following defects: (1) The oscillation conditions of the oscillator are relatively high and are not easy to meet; (2) It mainly uses a loop filter, and the setting of the loop filter will occupy a large chip area; (3) This technique first tunes the oscillation frequency of the loop oscillator through the phase-locked loop, and then gives the bias voltage generated by the VCO oscillation unit to the filter circuit, which belongs to continuous-time calibration. The setting of the phase-locked loop is likely to greatly increase the power consumption of the entire circuit system; (4) The oscillation signal of the oscillator leaks to the signal path of the filter, causing signal interference and reducing the filtering effect of the filter. The integral structure automatic tuning circuit is not as accurate as the phase-locked loop frequency tuning technique, but because this automatic tuning circuit only needs to perform power-on calibration, it is often used in occasions with low power consumption but low accuracy requirements, such as Figure 1 Shown is a commonly used existing integral structure automatic tuning circuit and a resistor array. Figure 1In the formula, Vref is the voltage under the condition of no deviation. The resistance is controlled by the traversal method. Since the maximum deviation may reach 50%, the tuning range of the resistance is set to 0.5R0 to 1.5R0 during control. The initial control string is 00000, and it traverses upward in turn. The working process of this automatic tuning circuit is as follows: First, close the switch S2 to reset the voltage of the capacitor to 0; open the switch S2 and close the switch S1. In this way, the power supply voltage VDD will charge the capacitor array through the switch S1 and the resistor R; after a fixed delay time T, if the voltage V of the capacitor is greater than the reference voltage Vref, it means that the time constant is too small, then increase the control word of the resistor, that is, increase the resistance. When the voltage on the resistor is less than the reference voltage, lock the control word and transmit the control word SW<4:0> to the resistor control bit of the reconfigurable transconductance conversion bias circuit. The automatic tuning circuit with this structure has a simple structure and is often used in active RC filters and modulators. However, in the gm-c structure filter or modulator, there are only gm units and capacitors. Using the existing above-mentioned integral structure automatic tuning circuit cannot perform bandwidth tuning on this gm-c structure circuit and cannot meet the usage requirements of the gm-c structure filter or modulator. Summary of the Invention

[0004] Aiming at the problem that the applicable range of the integral structure automatic tuning circuit in the prior art is relatively narrow and cannot meet the usage requirements of gm-c structure filters or modulators, the present invention provides a reconfigurable transconductance conversion bias circuit for tuning circuits and a method applying this circuit, which can realize gm unit tuning, so that the integral structure automatic tuning circuit can meet the usage requirements of filters or modulators with different structures, and can improve the applicable range of the automatic tuning circuit.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A reconfigurable transconductance conversion bias circuit, the bias circuit includes an amplifier, a gm unit, a capacitor, a switch, and a voltage source VDD. It is characterized in that the gm unit is in the form of a resistor, and it further includes a resistor R0 and a current mirror circuit. The current mirror circuit includes a first current mirror circuit and a second current mirror circuit. The voltage source VDD is respectively connected to the positive input terminal and the first current input terminal of the amplifier through the first current mirror circuit. The voltage source VDD is respectively connected to the negative input terminal and the second current input terminal of the amplifier through the second current mirror circuit. The second current mirror circuit is connected to the output terminal of the amplifier through the gm unit.

[0007] Its further features are as follows

[0008] The first current mirror circuit includes transistors M1 and M2, M3 and M4, M6 and M7 with their gates connected and mirror-distributed, and the second current mirror circuit includes transistors M8 and M9, M10 and M11, M13 and M14 with their gates connected and mirror-distributed;

[0009] The transistors M1 - M7 in the first current mirror circuit are of current mirror structure, and the transistors M8 - M14 in the second current mirror circuit are of current mirror structure;

[0010] The first current input terminal is connected to the gates of transistors M1 and M2 and the drain of transistor M1. The gates of transistors M3 and M4 are connected to the drain of transistor M6. The gates of transistors M6 and M7 are connected to the gate of transistor M5. The drain of transistor M2 is connected to the drain of transistor M5. The drain of transistor M4 is connected to the drains of transistor M7 and the positive input terminal of the amplifier through the resistor R0 respectively. The negative input terminal of the amplifier is connected to the drains of transistor M14 and the positive pole of the gm unit respectively. The gates of transistors M14 and M13 are connected to the gate of transistor M12. The drain of transistor M13 is connected to the bases of transistors M10 and M11 and the drain of transistor M10. The drain of transistor M11 is connected to the negative pole of the gm unit. The drain of transistor M12 is connected to the drain of transistor M9. The gates of transistors M9 and M8 are connected to the second current input terminal. The sources of transistors M5, M6, M7, M14, M13, M12 are connected to the voltage source VDD. The sources of transistors M1, M2, M3, M4, M11, M10, M9, M8 are grounded;

[0011] The transistors M1 - M4 and transistors M8 - M11 are all NMOS transistors, and the transistors M5, M6, M7, M12, M13, M14 are all PMOS transistors.

[0012] A method for tuning the center frequency and bandwidth by applying the above-mentioned reconfigurable transconductance conversion bias circuit to a filter or a modulator, characterized in that the method includes:

[0013] S1. External currents I1 and I2 are respectively fed into the bias circuit through the first current input terminal and the second current input terminal;

[0014] S2. The currents I1 and I2 are respectively mirrored to transistors M2 and M9 in proportion;

[0015] S3. Perform reconfigurable control on the filter or modulator. The reconfigurable control means controlling the current flowing through the gm cell and the resistor R0 through a current mirror control word, thereby controlling the gm value to change proportionally. At the same time, determine whether the voltages across the resistor R2 and the gm cell are the same or close.

[0016] S31. If the voltages are not the same, obtain the voltage difference between the two.

[0017] S32. Amplify the voltage difference through the amplifier to generate a corresponding bias voltage Vb, and feedback-tune the current of the gm cell through the bias voltage Vb until the bias voltage is stable and the voltages across the resistor R0 and the gm cell are equal.

[0018] It is further characterized in that

[0019] The current mirror control word includes 01 and 11. When the current mirror control word is 01, the bandwidth of the filter or modulator is + / -4 kHz, specifically + / -4 kHz on both sides of the center frequency of 3.1 kHz; when the current mirror control word is 11, the current mirrored to the resistor R0 is reduced to half of the original.

[0020] Calculate the gm value of the gm cell through the transconductance value formula. The transconductance value formula is:

[0021]

[0022] where gm is the transconductance value of the gm cell, i.e., the gm value, R 0 is the resistance value of the resistor R0, I gm is the current flowing through the gm cell, I R0 is the current flowing through the resistor R0; since the current I R0 mirrored to the resistor R0 is reduced to half of the original, therefore, through the transconductance value formula, the calculated gm value is also reduced to half of the original, making the bandwidth of the filter or modulator also reduced to half of the original.

[0023] S34. If the voltage at the positive input terminal of the amplifier is greater than the voltage at the negative input terminal, it indicates that the resistance value R 0 of the resistor R0 is greater than the reciprocal of the gm value, i.e., R0 > 1 / gm. After the voltage difference between the resistor R0 and the gm cell is amplified by the amplifier, a bias voltage for the gm cell is generated, the current flowing through the gm cell increases, and the gm value increases.

[0024] S35. If the voltage at the positive input terminal of the amplifier is smaller than the voltage at the negative input terminal, it indicates that the resistance value R of the resistor R0 0 is less than the reciprocal of the gm value, that is, R0 < 1 / gm. The voltage difference between the resistor R0 and the gm unit is amplified by the amplifier to generate the bias voltage of the gm unit, the current flowing through the gm unit decreases, and the gm value decreases.

[0025] Adopting the above structure of the present invention can achieve the following beneficial effects: 1. The reconfigurable transconductance conversion bias circuit includes a first current mirror circuit and a second current mirror circuit. The connection of the amplifier, gm unit, capacitor, switch, and voltage source VDD is realized through the first current mirror circuit and the second current mirror circuit. Since the gm unit is in the form of a resistor, and this circuit not only includes a gm unit and a capacitor unit, but also includes a first current mirror circuit, a second current mirror circuit, and an amplifier for tuning the gm unit. Therefore, by using the tunable function of the reconfigurable transconductance conversion bias circuit of the present application, the tuning of the gm unit and the capacitor can be converted into the tuning of the resistor and the capacitor. Thus, when this bias circuit is applied to the automatic tuning circuit of the integral structure, the automatic tuning circuit of the integral structure can meet the automatic tuning requirements of different structure filters or modulators, greatly improving the applicable range of this bias circuit and the automatic tuning circuit of the integral structure.

[0026] 2. When the bias circuit of the present invention is used to tune the center frequency and bandwidth in a filter or a modulator, through the first current mirror circuit, the second current mirror circuit, the amplifier, etc., the tuning of the gm unit and the capacitor can be converted into the tuning of the resistor and the capacitor, that is, the tuning of the time constant. In the tuning method of the present application, the filter or the modulator is reconfigurably controlled, that is, the current flowing through the gm unit and the resistor R0 can be controlled by the current mirror control word, so as to control the gm value to change proportionally. Since the value of the gm unit in this bias circuit is adjustable, it can meet the automatic tuning requirements of different structure filters or modulators, and the flexibility and applicable range of use are greatly improved. Description of the Drawings

[0027] Figure 1 is the circuit schematic diagram of the automatic tuning circuit of the integral structure and the capacitor array in the prior art;

[0028] Figure 2 is the circuit schematic diagram of the reconfigurable transconductance conversion bias circuit of the present invention;

[0029] Figure 3 is the response curve diagram of the center frequency and bandwidth amplitude after applying the present invention to a complex band-pass filter;

[0030] Figure 4Response curves of the center frequency and bandwidth at the SS, TT, and FF process corners for applying the present invention to an automatic tuning circuit of an integration structure. Detailed implementation manner

[0031] See Figure 2 A reconfigurable transconductance conversion bias circuit for a tuning circuit. The bias circuit includes an amplifier, a gm unit, a capacitor, a switch, a voltage source VDD, a resistor R0, and a current mirror circuit. The gm unit is in the form of a resistor. The current mirror circuit includes a first current mirror circuit 1 and a second current mirror circuit 2. The voltage source VDD is connected to the positive input terminal and the first current input terminal of the amplifier through the first current mirror circuit 1 respectively. The voltage source VDD is connected to the negative input terminal and the second current input terminal of the amplifier through the second current mirror circuit 2 respectively. The second current mirror circuit 2 is connected to the output terminal of the amplifier through the gm unit.

[0032] The first current mirror circuit 1 includes transistors M1 and M2 with their gates connected and mirror-distributed, transistors M3 and M4 with their gates connected and mirror-distributed, and transistors M6 and M7 with their gates connected and mirror-distributed. The second current mirror circuit includes transistors M8 and M9 with their gates connected and mirror-distributed, transistors M10 and M11 with their gates connected and mirror-distributed, and transistors M13 and M14 with their gates connected and mirror-distributed. The transistors M1 to M7 in the first current mirror circuit and the transistors M8 to M14 in the second current mirror circuit are in a parallel array structure (i.e., a current mirror structure). The transistors M1 to M4 and the transistors M8 to M11 are all NMOS transistors. The transistors M5, M6, M7, M12, M13, and M14 are all PMOS transistors.

[0033] The first current input terminal is connected to the gates of transistors M1 and M2, the drain of transistor M1, the gates of transistors M3 and M4 are connected to the drain of transistor M6, the gates of transistors M6 and M7 are connected to the gate of transistor M5, the drain of transistor M2 is connected to the drain of transistor M5, the drain of transistor M4 is connected to the drains of transistor M7 and the positive input terminal of the amplifier through resistor R0 respectively, the negative input terminal of the amplifier is connected to the drains of transistor M14 and the positive terminal of the gm unit respectively, the gates of transistors M14 and M13 are connected to the gate of transistor M12, the drain of transistor M13 is connected to the bases of transistors M10 and M11 and the drain of transistor M10, the drain of transistor M11 is connected to the negative terminal of the gm unit, the drain of transistor M12 is connected to the drain of transistor M9, the gates of transistors M9 and M8 are connected to the second current input terminal, the sources of transistors M5, M6, M7, M14, M13, M12 are connected to the voltage source VDD, and the sources of transistors M1, M2, M3, M4, M11, M10, M9, M8 are grounded, where transistors M5 and M12 are adjustable transistor arrays and resistor R0 is an adjustable resistor.

[0034] A method for tuning the center frequency and bandwidth by applying the above-mentioned reconfigurable transconductance conversion bias circuit to a filter or a modulator, the method includes:

[0035] S1. External currents I1 and I2 are respectively fed into the bias circuit through the first current input terminal and the second current input terminal;

[0036] S2. Currents I1 and I2 are respectively mirrored to transistors M2 and M9 in proportion;

[0037] S3. Perform reconfigurable control on the filter or the modulator. In the reconfigurable transconductance conversion bias circuit used for tuning the circuit, the gm unit is connected in the form of a resistor. A current mirror circuit is formed by M1 and M2 to mirror the external input current I1 to the NMOS transistor M2 in proportion. Correspondingly, a current mirror circuit is formed by M8 and M9 to mirror the external input current I2 to the NMOS transistor M9 in proportion. M5 and M12 are PMOS arrays in a parallel structure. The currents mirrored from M5 and M12 to M6 and M13 are controlled by switches T1<1:0> and T2<1:0>.

[0038] The reconfigurable control means controlling the currents flowing through the gm unit and resistor R0 through the current mirror control word, that is, controlling the currents mirrored from transistors M5 and M12 to transistors M6 and M13 through switches T1<1:0> and T2<1:0>, so as to control the gm value to change proportionally. At the same time, it is judged whether the voltages across resistor R2 and the gm unit are the same. The voltages across resistor R0 and the gm unit should be the same.

[0039] S31. If they are not the same, obtain the voltage difference between the two;

[0040] S32. Amplify the voltage difference through an amplifier to generate a corresponding bias voltage Vb, and feedback-tune the current of the gm cell through the bias voltage Vb. During the tuning process, calculate the gm value of the gm cell. The gm value is obtained through the transconductance value formula, and the transconductance value formula is:

[0041]

[0042] where gm is the transconductance value of the gm cell, that is, the gm value, R 0 is the resistance value of resistor R0, I gm is the current flowing through the gm cell, I R0 is the current flowing through resistor R0; if the current I R0 mirrored to resistor R0 is reduced to half of the original, I gm , R 0 remains unchanged, then the gm value obtained through the transconductance value formula is also reduced to half of the original, so that the bandwidth of the filter or modulator is also reduced to half of the original. Conversely, the bandwidth of the filter or modulator increases. During the tuning process, if the voltage at the positive input terminal of the amplifier is greater than the voltage at the negative input terminal, it means that the resistance value R 0 of resistor R0 is greater than the reciprocal of the gm value, that is, R0 > 1 / gm. After the voltage difference between resistor R0 and the gm cell is amplified by the amplifier, a bias voltage of the gm cell is generated, and the current flowing through the gm cell increases, and the gm value increases; conversely, the gm value decreases; adopting the above step S3 method, the gm cell is repeatedly adjusted through the current mirror control word until the bias voltage V b is stable, and the voltages at both ends of resistor R0 and the gm cell are equal.

[0043] When controlling the currents flowing through the gm cell and resistor R0 through switches T1<1:0>, T2<1:0> and the current mirror control word, the current mirror control word includes 01 and 11. When the current mirror control word is 01, the bandwidth amplitude response of the filter is as Figure 3 shown, Figure 3 where the horizontal axis represents frequency, the vertical axis represents the bandwidth amplitude gain, the center frequency is 3.1 kHz, the bandwidth is + / -4 kHz (4 kHz on both sides of the center frequency 3.1 kHz, that is, the frequency range is 3.1 kHz - 4 kHz to 3.1 kHz + 4 kHz), and the passband gain is 0 dB (at this time, the signal passing through the filter has neither gain nor attenuation); when the current mirror control word is 11, the current mirrored to resistor R0 is reduced to half of the original. It can be calculated through the above transconductance value formula that the gm value becomes twice the original. At this time, the bandwidth of the filter also becomes twice the original accordingly. The bandwidth change is as Figure 3As shown: center frequency 3.1kHz, bandwidth is + / -8kHz (+ / -8kHz on both sides of the center frequency 3.1kHz, that is, the frequency range is 3.1kHz-8kHz~3.1kHz+8kHz), and the passband gain is 0dB.

[0044] The reconfigurable transconductance conversion bias circuit of the present invention is applied to a filter or modulator with a gm-c structure. The bias circuit and tuning method of the present invention convert the tuning of the gm unit and capacitor into the tuning of the resistor and capacitor, that is, the tuning of the time constant. By changing the control word of the current mirror array, the center frequency and bandwidth of the filter and modulator can be reconstructed, thereby meeting the use requirements of the filter or modulator with a gm-c structure. When the bias circuit is applied to a filter or modulator with a gm-c structure as an automatic tuning circuit, the bandwidth response under different process angles is as follows: Figure 4 As shown, Figure 4 The horizontal axis represents frequency, and the vertical axis represents bandwidth gain. Figure 3 It can also be seen that under the SS, FF and TT process angles, the bandwidth variation of two adjacent curves is within 7%, that is, the deviation of the center frequency and bandwidth can be reduced from the existing theoretical 50% to within 7%, indicating that the voltage deviation across the resistor R2 and the gm unit is greatly reduced, which can meet the use requirements of the gm-c structure filter or modulator.

[0045] The above are only preferred embodiments of the present application, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.

Claims

1. A bandwidth tuning method, which is used for a filter or a modulator, and is based on a reconfigurable transconductance conversion bias circuit, where the reconfigurable transconductance conversion bias circuit includes an amplifier, a gm cell, a capacitor, a switch, and a voltage source VDD. Characterized in that: The reconfigurable transconductance conversion bias circuit further includes a resistor R0, a resistor R2, and a current mirror circuit. The current mirror circuit includes a first current mirror circuit and a second current mirror circuit. The voltage source VDD is connected to the positive input terminal and the first current input terminal of the amplifier through the first current mirror circuit respectively. The voltage source VDD is connected to the negative input terminal and the second current input terminal of the amplifier through the second current mirror circuit respectively. The second current mirror circuit is connected to the output terminal of the amplifier through the gm cell. The first current mirror circuit includes transistors M1 and M2, M3 and M4, M6 and M7 whose gates are connected and mirror-distributed, and the first current mirror circuit further includes M5. The second current mirror circuit includes transistors M8 and M9, M10 and M11, M13 and M14 whose gates are connected and mirror-distributed, and the second current mirror circuit further includes M12. The transistors M1-M7 in the first current mirror circuit are of a current mirror structure, and the transistors M8-M14 in the second current mirror circuit are of a current mirror structure. The first current input terminal is connected to the gates of transistors M1 and M2 and the drain of transistor M1. The gates of transistors M3 and M4 are connected to the drain of transistor M6. The gates of transistors M6 and M7 are connected to the gate of transistor M5. The drain of transistor M2 is connected to the drain of transistor M5. The drain of transistor M4 is connected to the drain of transistor M7 and the positive input terminal of the amplifier through the resistor R0 respectively. The negative input terminal of the amplifier is connected to the drain of transistor M14 and the positive pole of the gm cell respectively. The gates of transistors M14 and M13 are connected to the gate of transistor M12. The drain of transistor M13 is connected to the gates of transistors M10 and M11 and the drain of transistor M10. The drain of transistor M11 is connected to the negative pole of the gm cell. The drain of transistor M12 is connected to the drain of transistor M9. The gates of transistors M9 and M8 are connected to the second current input terminal. The sources of transistors M5, M6, M7, M14, M13, and M12 are connected to the voltage source VDD. The sources of transistors M1, M2, M3, M4, M11, M10, M9, and M8 are grounded. The bandwidth tuning method includes: External currents I1 and I2 are respectively fed into the bias circuit through the first current input terminal and the second current input terminal. The currents I1 and I2 are respectively mirrored to transistors M2 and M9 in proportion. Perform reconfigurable control on the filter or modulator. The reconfigurable control refers to controlling the current flowing through the gm cell and the resistor R0 through a current mirror control word, so as to control the gm value to change proportionally. At the same time, determine whether the voltages across the resistor R2 and the gm cell are the same or close: If the voltages are not the same, obtain the voltage difference between the two; Amplify the voltage difference through the amplifier to generate a corresponding bias voltage Vb, and feedback-tune the current of the gm cell through the bias voltage Vb until the bias voltage is stable and the voltages across the resistor R0 and the gm cell are equal.

2. The bandwidth tuning method according to claim 1, wherein, the current mirror control word includes 01 and 11. When the current mirror control word is 01, the bandwidth response of the filter or modulator is + / -4 kHz; when the current mirror control word is 11, the current mirrored to the resistor R0 is reduced to half of the original, and the bandwidth of the filter or modulator is correspondingly increased to + / -8 kHz.

3. The bandwidth tuning method according to claim 2, wherein, calculate the gm value passing through the gm cell through the transconductance value formula, and the transconductance value formula is: wherein, gm is the transconductance value of the gm unit, i.e., the gm value, and R 0 is the resistance value of the resistor R0, and I gm is the current flowing through the gm unit, and I R0 is the current flowing through the resistor R0.

4. The bandwidth tuning method according to claim 3, wherein, If the voltage at the positive input terminal of the amplifier is greater than the voltage at the negative input terminal, it indicates that the resistance value R of the resistor R0 0 is greater than the reciprocal of the gm value, that is, R0 > 1 / gm. After the voltage difference between the resistor R0 and the gm unit is amplified by the amplifier, the bias voltage of the gm unit is generated, the current flowing through the gm unit increases, and the gm value increases; conversely, the gm value decreases.

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