Power supply noise suppression circuit

Abstract

The invention discloses a power supply noise suppression circuit, which comprises a tuning gain unit, the tuning gain unit is connected in parallel with a frequency regulation circuit of an oscillator, the tuning gain unit is used for providing tuning gain, and the polarity of the tuning gain is opposite to that of the power supply sensitivity of the oscillator.

Description

Technical Field

[0001] This application relates to the technical field of oscillators, and particularly to a power supply noise suppression circuit. Background Art

[0002] Modern systems-on-chip integrate radio frequency, analog, mixed-signal, and digital subsystems on a single chip. The dynamic current demands of different functional modules cause power supply voltage fluctuations. Due to limited power supply isolation, sensitive circuits are vulnerable to power supply ripple interference from other modules. In addition, the output noise of the power management circuit also appears as random perturbations of the power supply voltage. Radio frequency oscillators are usually the most sensitive to power supply fluctuations, and their low-frequency perturbations modulate the oscillation frequency through the phase accumulation effect. Therefore, the power supply immunity of oscillators is not high. Summary of the Invention

[0003] This application aims to propose a power supply noise suppression circuit that can improve the power supply immunity of oscillators.

[0004] An embodiment of this application provides a power supply noise suppression circuit, including:

[0005] A tuning gain unit, the tuning gain unit is connected in parallel with the frequency adjustment circuit of the oscillator, the tuning gain unit is used to provide a tuning gain, and the polarity of the tuning gain is opposite to the polarity of the power supply sensitivity of the oscillator.

[0006] According to some embodiments of this application, the tuning gain unit includes a first varactor sub-unit and / or a second varactor sub-unit, where

[0007] The first varactor sub-unit is connected in parallel with the frequency adjustment circuit, and the first varactor sub-unit is used to provide the tuning gain with a positive polarity when the polarity of the power supply sensitivity of the oscillator is negative;

[0008] The second varactor sub-unit is connected in parallel with the frequency adjustment circuit, and the second varactor sub-unit, the first varactor sub-unit is used to provide the tuning gain with a negative polarity when the polarity of the power supply sensitivity of the oscillator is positive.

[0009] According to some embodiments of this application, the first varactor sub-unit includes:

[0010] A first varactor diode, the cathode of the first varactor diode is connected to the first end of the frequency adjustment circuit;

[0011] A second varactor diode, the anode of the second varactor diode is connected to the anode of the first varactor diode, and the cathode of the second varactor diode is connected to the second end of the frequency adjustment circuit.

[0012] According to some embodiments of the present application, a first capacitor is disposed between the cathode of the first varactor diode and the first terminal, and a second capacitor is disposed between the cathode of the second varactor diode and the second terminal of the frequency adjustment circuit.

[0013] According to some embodiments of the present application, the second varactor sub-unit includes:

[0014] A third varactor diode, the anode of the third varactor diode is connected to the first terminal of the frequency adjustment circuit;

[0015] A fourth varactor diode, the cathode of the fourth varactor diode is connected to the cathode of the third varactor diode, and the anode of the fourth varactor diode is connected to the second terminal of the frequency adjustment circuit.

[0016] According to some embodiments of the present application, a third capacitor is disposed between the anode of the third varactor diode and the first terminal, and a fourth capacitor is disposed between the anode of the fourth varactor diode and the second terminal of the frequency adjustment circuit.

[0017] According to some embodiments of the present application, the tuning gain unit further includes:

[0018] A first gain calibration sub-unit, the first gain calibration sub-unit is connected to the first varactor sub-unit, and the first gain calibration sub-unit is used to adjust the tuning gain with positive polarity;

[0019] A second gain calibration sub-unit, the second gain calibration sub-unit is connected to the second varactor sub-unit, and the second gain calibration sub-unit is used to adjust the tuning gain with negative polarity.

[0020] According to some embodiments of the present application, the first gain calibration sub-unit includes:

[0021] A fifth capacitor, the first terminal of the fifth capacitor is connected to the power supply terminal, and the second terminal of the fifth capacitor is connected to the first varactor sub-unit;

[0022] A sixth capacitor, the first terminal of the sixth capacitor is connected to the second terminal of the fifth capacitor, and the second terminal of the sixth capacitor is grounded.

[0023] According to some embodiments of the present application, the second gain calibration sub-unit includes:

[0024] A seventh capacitor, the first terminal of the seventh capacitor is connected to the power supply terminal, and the second terminal of the seventh capacitor is connected to the second varactor sub-unit;

[0025] An eighth capacitor, the first terminal of the eighth capacitor is connected to the second terminal of the seventh capacitor, and the second terminal of the eighth capacitor is grounded.

[0026] According to some embodiments of the present application, it further includes:

[0027] A low-pass filter, which is disposed between the power supply terminal and the control circuit of the frequency adjustment circuit.

[0028] In a second aspect, an embodiment of the present application discloses an oscillator, including the power supply noise suppression circuit as described above.

[0029] In the embodiment of the present application, by connecting a tuning gain unit in parallel to the frequency adjustment circuit sensitive to power supply noise, and using the tuning gain unit to provide a tuning gain with a polarity opposite to the power supply sensitivity of the oscillator, the power supply sensitivity is thus cancelled out, and the power supply immunity of the oscillator is improved.

[0030] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present application. Description of the Drawings

[0031] The following further describes the present application with reference to the drawings and embodiments, where:

[0032] Figure 1 is a schematic circuit diagram of the power supply noise suppression circuit applied to an LC oscillator in the embodiment of the power supply noise suppression circuit provided by the present application;

[0033] Figure 2 is the phase noise measured by the oscillator at different oscillation frequencies in the embodiment of the power supply noise suppression circuit provided by the present application;

[0034] Figure 3 is the measurement result of the spurious level caused by the power supply ripple of the oscillator at different α values in the embodiment of the power supply noise suppression circuit provided by the present application;

[0035] Figure 4 is the output spectrum of an oscillator without using the power supply noise suppression circuit provided by the present application;

[0036] Figure 5 is the output spectrum of an oscillator using the power supply noise suppression circuit provided by the present application;

[0037] Figure 6 is a graph of the measurement results of the spurious levels of the oscillator before and after using the power supply noise suppression circuit provided by the present application;

[0038] Figure 7 is a graph of the measurement results of the output spurious levels of the oscillator after using the power supply noise suppression circuit provided by the present application;

[0039] Figure 8 is the power spectral density graph of the oscillator after injecting excessive noise into the power supply of the oscillator;

[0040] Figure 9 The power spectral density diagram of the oscillator after adopting the power noise suppression circuit provided by this application;

[0041] Figure 10 The phase noise diagram of the oscillator measured under three different conditions;

[0042] Figure 11 The frequency modulation demodulation signal diagram of the oscillator.

[0043] Reference numerals:

[0044] Frequency adjustment circuit 100, control circuit 200. Detailed implementation manners

[0045] The following details the embodiments of this application. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are only used to explain this application and should not be construed as a limitation to this application.

[0046] In the description of this application, it should be understood that the orientation descriptions such as up and down refer to the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. This is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to this application.

[0047] In the description of this application, "a plurality of" means more than two. If there is a description of first and second, it is only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence relationship of the indicated technical features.

[0048] In the description of this application, unless otherwise clearly defined, words such as "set", "installed", and "connected" should be understood in a broad sense. Those skilled in the art can reasonably determine the specific meanings of the above words in this application in combination with the specific content of the technical solution.

[0049] The following is based on Figures 1 to 11 Describe a power noise suppression circuit provided by an embodiment of this application.

[0050] An embodiment of this application provides a power noise suppression circuit, including:

[0051] A tuning gain unit, the tuning gain unit is connected in parallel with the frequency adjustment circuit 100 of the oscillator. The tuning gain unit is used to provide a tuning gain, and the tuning gain is opposite in polarity to the power supply sensitivity of the oscillator.

[0052] In the embodiments of the present application, by connecting a tuning gain unit in parallel to the frequency adjustment circuit 100 sensitive to power supply noise, and using the tuning gain unit to provide a tuning gain with the opposite polarity to the power supply sensitivity of the oscillator, the power supply sensitivity is cancelled, thereby improving the power supply immunity of the oscillator.

[0053] In some embodiments of the present application, the power supply noise suppression circuit can be applied to any type of oscillator, such as: voltage-biased oscillators and current-biased oscillators. Specifically, such as LC oscillators, ring oscillators, etc.

[0054] In some embodiments of the present application, the frequency adjustment circuit 100 of the oscillator is a circuit for adjusting the frequency of the oscillator. The frequency adjustment circuit 100 can use devices such as switched capacitors and varactor diodes to adjust the frequency of the oscillator.

[0055] In some embodiments of the present application, the tuning gain unit includes a first varactor sub-unit and / or a second varactor sub-unit, wherein,

[0056] The first varactor sub-unit is connected in parallel to the frequency adjustment circuit 100, and the first varactor sub-unit is used to provide a positive-polarity tuning gain when the polarity of the power supply sensitivity of the oscillator is negative;

[0057] The second varactor sub-unit is connected in parallel to the frequency adjustment circuit 100. The second varactor sub-unit and the first varactor sub-unit are used to provide a negative-polarity tuning gain when the polarity of the power supply sensitivity of the oscillator is positive.

[0058] In this embodiment, if it is determined that the polarity of the power supply sensitivity of the oscillator is negative, the tuning gain unit includes a first varactor sub-unit, and the first varactor sub-unit is used to provide a positive-polarity tuning gain to cancel the negative-polarity power supply sensitivity of the oscillator. If it is determined that the polarity of the power supply sensitivity of the oscillator is positive, the tuning gain unit includes a second varactor sub-unit, and the second varactor sub-unit is used to provide a negative-polarity tuning gain to cancel the positive-polarity power supply sensitivity of the oscillator.

[0059] In some embodiments of the present application, the tuning gain unit can also include both a first varactor sub-unit and a second varactor sub-unit. When it is determined that the polarity of the power supply sensitivity of the oscillator is negative, the first varactor sub-unit is controlled to work, and the second varactor sub-unit is controlled not to work. When it is determined that the polarity of the power supply sensitivity of the oscillator is positive, the second varactor sub-unit is controlled to work, and the first varactor sub-unit is controlled not to work.

[0060] In some embodiments of the present application, the polarity of the power supply sensitivity of the oscillator can be determined by applying a well-defined ripple (such as a square wave with a fixed frequency) to the power supply voltage and checking the direction of the frequency modulation of the oscillator.

[0061] In some embodiments of the present application, as Figure 1 shown, the first varactor sub-unit includes:

[0062] A first varactor diode D1, the cathode of the first varactor diode D1 is connected to the first end of the frequency adjustment circuit 100;

[0063] A second varactor diode D2, the anode of the second varactor diode D2 is connected to the anode of the first varactor diode D1, and the cathode of the second varactor diode D2 is connected to the second end of the frequency adjustment circuit 100.

[0064] In this embodiment, the first varactor diode D1 and the second varactor diode D2 form a varactor with a positive polarity. The power supply sensitivity of the varactor with a positive polarity is positive. Therefore, it can provide a positive tuning gain to offset the negative power supply sensitivity of the oscillator.

[0065] In some embodiments of the present application, as Figure 1 shown, by configuring a bias voltage for the varactor with a positive polarity, the varactor with a positive polarity is in the sensitive range, so as to control the operation of the varactor with a positive polarity and provide a positive tuning gain.

[0066] In some embodiments of the present application, a first capacitor C5 is provided between the cathode and the first end of the first varactor diode D1, and a second capacitor C6 is provided between the cathode of the second varactor diode D2 and the second end of the frequency adjustment circuit 100.

[0067] In this embodiment, the first varactor diode D1 and the second varactor diode D2 are AC-coupled to the oscillator through the first capacitor C5 and the second capacitor C6. The power supply change will be coupled to the first varactor diode D1 and the second varactor diode D2 through the first capacitor C5 and the second capacitor C6. The corresponding tuning gain is generated by the first varactor diode D1 and the second varactor diode D2 to improve the power supply immunity of the oscillator.

[0068] In some embodiments of the present application, as Figure 1 shown, the second varactor sub-unit includes:

[0069] A third varactor diode D3, the anode of the third varactor diode D3 is connected to the first end of the frequency adjustment circuit 100;

[0070] The fourth varactor diode D4, the cathode of the fourth varactor diode D4 is connected to the cathode of the third varactor diode D3, and the anode of the fourth varactor diode D4 is connected to the second terminal of the frequency adjustment circuit 100.

[0071] In this embodiment, the third varactor diode D3 and the fourth varactor diode D4 form a varactor with a negative polarity. The power supply sensitivity of the varactor with a negative polarity is negative. Therefore, a negative tuning gain can be provided to offset the positive power supply sensitivity of the oscillator.

[0072] In some embodiments of the present application, as Figure 1 shown, by configuring a bias voltage for the varactor with a negative polarity, the varactor with a negative polarity is in the sensitive range, so as to control the operation of the varactor with a negative polarity and provide a negative tuning gain.

[0073] In some embodiments of the present application, as Figure 1 shown, a third capacitor is provided between the anode and the first terminal of the third varactor diode D3, and a fourth capacitor is provided between the anode of the fourth varactor diode D4 and the second terminal of the frequency adjustment circuit 100.

[0074] In some embodiments of the present application, if the tuning gain unit includes both the first varactor sub-unit and the second varactor sub-unit at the same time, both the first varactor sub-unit and the second varactor sub-unit are AC-coupled to the oscillator through the first capacitor C5 and the second capacitor C6, and there is no need to provide the third capacitor and the fourth capacitor.

[0075] In this embodiment, the third varactor diode D3 and the fourth varactor diode D4 are AC-coupled to the oscillator through the third capacitor and the fourth capacitor. The power supply change will be coupled to the third varactor diode D3 and the fourth varactor diode D4 through the third capacitor and the fourth capacitor, and the corresponding tuning gain is generated by using the third varactor diode D3 and the fourth varactor diode D4 to improve the power supply immunity of the oscillator.

[0076] In some embodiments of the present application, the tuning gain unit further includes:

[0077] A first gain calibration sub-unit, the first gain calibration sub-unit is connected to the first varactor sub-unit, and the first gain calibration sub-unit is used to adjust the positive tuning gain;

[0078] A second gain calibration sub-unit, the second gain calibration sub-unit is connected to the second varactor sub-unit, and the second gain calibration sub-unit is used to adjust the negative tuning gain.

[0079] In this embodiment, the first gain calibration subunit is used to adjust the first coupling coefficient of the power supply change input to the first varactor subunit, so as to adjust the magnitude of the tuning gain in the positive polarity, so that the power supply sensitivity in the negative polarity can be eliminated by the tuning gain in the positive polarity. The second gain calibration subunit is used to adjust the second coupling coefficient of the power supply change input to the second varactor subunit, so as to adjust the magnitude of the tuning gain in the negative polarity, so that the power supply sensitivity in the positive polarity can be eliminated by the tuning gain in the negative polarity.

[0080] In some embodiments of the present application, as Figure 1 shown, the first gain calibration subunit includes:

[0081] A fifth capacitor C1, the first end of the fifth capacitor C1 is connected to the power supply terminal, and the second end of the fifth capacitor C1 is connected to the first varactor subunit;

[0082] A sixth capacitor C2, the first end of the sixth capacitor C2 is connected to the second end of the fifth capacitor C1, and the second end of the sixth capacitor C2 is grounded.

[0083] In this embodiment, the fifth capacitor C1 and the sixth capacitor C2 form a capacitive voltage divider for capacitive voltage division, so as to adjust the first coupling coefficient. The first coupling coefficient is calculated by the following formula:

[0084]

[0085] where α1 is the first coupling coefficient, C 11 is the capacitance value of the fifth capacitor C1, and C 12 is the capacitance value of the sixth capacitor C2.

[0086] In some embodiments of the present application, both the fifth capacitor C1 and the sixth capacitor C2 are switch capacitors.

[0087] In some embodiments of the present application, as Figure 1 shown, the second gain calibration subunit includes:

[0088] A seventh capacitor C4, the first end of the seventh capacitor C4 is connected to the power supply terminal, and the second end of the seventh capacitor C4 is connected to the second varactor subunit;

[0089] An eighth capacitor C3, the first end of the eighth capacitor C3 is connected to the second end of the seventh capacitor C4, and the second end of the eighth capacitor C3 is grounded.

[0090] In this embodiment, the seventh capacitor C4 and the eighth capacitor C3 form a capacitive voltage divider for capacitive voltage division, so as to adjust the second coupling coefficient. The second coupling coefficient is calculated by the following formula:

[0091]

[0092] where α2 is the second coupling coefficient, C 21 is the capacitance value of the fifth capacitor C1, C 22 is the capacitance value of the sixth capacitor C2.

[0093] In some embodiments of the present application, both the seventh capacitor C4 and the eighth capacitor C3 are switched capacitors.

[0094] In some embodiments of the present application, it further includes:

[0095] A low-pass filter, which is disposed between the power supply terminal and the control circuit 200 of the frequency adjustment circuit 100.

[0096] In this embodiment, in the frequency adjustment circuit 100 of the oscillator, for example, a switched capacitor, there is power supply sensitivity caused by code-dependent parasitic capacitance. The low-pass filter is used to suppress the power supply sensitivity caused by the code-dependent parasitic capacitance of the switched capacitor.

[0097] In some embodiments of the present application, as Figure 1 shown, the low-pass filter includes:

[0098] A resistor RL, the first end of the resistor RL is connected to the power supply terminal, and the second end of the resistor RL is connected to the control circuit 200 of the frequency adjustment circuit 100;

[0099] A ninth capacitor CL, the first end of the ninth capacitor CL is connected to the second end of the resistor RL, and the second end of the ninth capacitor CL is grounded.

[0100] In this embodiment, the resistor RL and the ninth capacitor CL form a low-pass filter to reduce the power supply sensitivity of the switched capacitor in the frequency adjustment circuit 100.

[0101] In addition, the embodiments of the present application disclose an oscillator, including the power supply noise suppression circuit as described above.

[0102] The oscillator provided by the embodiments of the present application implements each process implemented by the above circuit embodiments and achieves the same beneficial effects. To avoid repetition, it will not be elaborated here.

[0103] Next, the test results of the oscillator using the power supply noise suppression circuit provided by the present application will be specifically described.

[0104] As Figure 2 shown, Figure 2 shows the phase noise measured by the oscillator at different oscillation frequencies. It can be seen that at a 10 MHz offset, the phase noise range is -137.2 to -139.4 dBc / Hz, covering the entire frequency tuning range.

[0105] As Figure 3 shown, Figure 3Shows the measurement results of the spurious level caused by power supply ripple of the oscillator at different values of α (the first coupling coefficient or the second coupling coefficient). When α is set to the optimal value of 0.63, the spurious level is reduced from -34 dBc to -77.5 dBc, and the power supply sensitivity is reduced by 43.5 dB.

[0106] As Figures 4 to 5 shown, where Figure 4 is the output spectrum of the oscillator without the power supply noise suppression circuit provided by the present application, Figure 5 is the output spectrum of the oscillator with the power supply noise suppression circuit provided by the present application. Comparing Figure 4 and Figure 5 it can be seen that the spurious level of the oscillator with the power supply noise suppression circuit provided by the present application is significantly reduced.

[0107] As Figure 6 shown, Figure 6 shows the spurious level of the oscillator measured before and after using the power supply noise suppression circuit provided by the present application within the entire frequency tuning range, as well as the achieved reduction in power supply sensitivity, with the overall reduction in power supply sensitivity exceeding 42 dB.

[0108] As Figure 7 shown, Figure 7 shows the output spurious level of the oscillator after using the power supply noise suppression circuit provided by the present application. According to Figure 7 it is known that within the frequency range where the ripple is applied, the maximum value of the spurious level is 46.2 dB.

[0109] Excessive noise is injected into the power supply of the oscillator, and the power spectral density of the oscillator is as Figure 8 shown. As Figure 9 shown, after using the power supply noise suppression circuit provided by the present application, the phase noise caused by the power supply noise is greatly suppressed.

[0110] As Figure 10 shown, after using the power supply noise suppression circuit provided by the present application, under three different cancellation conditions, the attenuation of the phase noise is not obvious, indicating that the reduction of the Q factor of the oscillator is negligible.

[0111] In the case where a square wave is applied to the power supply voltage, the frequency demodulation signal of the oscillator is measured as Figure 11 shown. Figure 11 Shows the results in three cases: before cancellation, optimal cancellation, and over cancellation.

[0112] It can be seen from the above test results that since the power supply noise suppression circuit of the present application adopts a fully passive power supply noise suppression method, it will not generate additional power consumption and will not cause attenuation of phase noise, greatly improving the power supply immunity of the oscillator.

[0113] The embodiments of the present application have been described in detail above with reference to the accompanying drawings. However, the present application is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present application within the scope of knowledge possessed by those of ordinary skill in the art.

Claims

1. A power supply noise suppression circuit, characterized in that, Comprising: A tuning gain unit, which is connected in parallel with the frequency adjustment circuit of the oscillator. The tuning gain unit is used to provide a tuning gain, and the tuning gain has a polarity opposite to that of the power supply sensitivity of the oscillator.

2. The power supply noise suppression circuit according to claim 1, wherein The tuning gain unit includes a first varactor sub-unit and / or a second varactor sub-unit, where The first varactor sub-unit is connected in parallel with the frequency adjustment circuit. The first varactor sub-unit is used to provide the tuning gain with a positive polarity when the polarity of the power supply sensitivity of the oscillator is negative. The second varactor sub-unit is connected in parallel with the frequency adjustment circuit. The second varactor sub-unit, the first varactor sub-unit is used to provide the tuning gain with a negative polarity when the polarity of the power supply sensitivity of the oscillator is positive.

3. The power supply noise suppression circuit according to claim 2, characterized in that, The first varactor sub-unit includes: A first varactor diode, the cathode of the first varactor diode is connected to the first end of the frequency adjustment circuit; A second varactor diode, the anode of the second varactor diode is connected to the anode of the first varactor diode, and the cathode of the second varactor diode is connected to the second end of the frequency adjustment circuit.

4. The power supply noise suppression circuit according to claim 3, characterized in that: A first capacitor is provided between the cathode of the first varactor diode and the first end, and a second capacitor is provided between the cathode of the second varactor diode and the second end of the frequency adjustment circuit.

5. The power supply noise suppression circuit according to claim 2, wherein The second varactor sub-unit includes: A third varactor diode, the anode of the third varactor diode is connected to the first end of the frequency adjustment circuit; A fourth varactor diode, the cathode of the fourth varactor diode is connected to the cathode of the third varactor diode, and the anode of the fourth varactor diode is connected to the second end of the frequency adjustment circuit.

6. The power supply noise suppression circuit according to claim 5, characterized in that: A third capacitor is provided between the anode of the third varactor diode and the first end, and a fourth capacitor is provided between the anode of the fourth varactor diode and the second end of the frequency adjustment circuit.

7. The power supply noise suppression circuit according to claim 2, wherein The tuning gain unit further includes: A first gain calibration sub-unit, which is connected to the first varactor sub-unit. The first gain calibration sub-unit is used to adjust the tuning gain with a positive polarity; A second gain calibration sub-unit, which is connected to the second varactor sub-unit. The second gain calibration sub-unit is used to adjust the tuning gain with a negative polarity.

8. The power supply noise suppression circuit according to claim 7, wherein The first gain calibration sub-unit includes: A fifth capacitor, the first end of the fifth capacitor is connected to the power supply terminal, and the second end of the fifth capacitor is connected to the first varactor sub-unit; A sixth capacitor, the first end of the sixth capacitor is connected to the second end of the fifth capacitor, and the second end of the sixth capacitor is grounded.

9. The power supply noise suppression circuit according to claim 7, characterized in that, The second gain calibration sub-unit includes: A seventh capacitor, the first end of the seventh capacitor is connected to the power supply terminal, and the second end of the seventh capacitor is connected to the second varactor sub-unit; An eighth capacitor, the first end of the eighth capacitor is connected to the second end of the seventh capacitor, and the second end of the eighth capacitor is grounded.

10. The power supply noise suppression circuit according to claim 1, characterized in that, Also included: A low-pass filter, the low-pass filter being disposed between a power supply terminal and a control circuit of a frequency adjustment circuit.

Images