A low-noise LDO circuit

Abstract

The present invention discloses a low-noise LDO circuit, comprising: a bandgap reference circuit, which improves the output reference voltage of the bandgap reference circuit by connecting the reverse-biased diodes in the triode in series. The present invention adopts a low-noise bandgap reference circuit structure capable of outputting a relatively high voltage, reduces the amplification factor of the reference voltage noise to the output end, and realizes low-noise output in the full frequency band without using a filter capacitor.

Description

Technical Field

[0001] This application relates to the field of integrated circuit design, and particularly to a low-noise LDO circuit. Background Art

[0002] In contemporary electronic systems, the low dropout regulator (LDO), as a core component of the power management module, its output noise characteristics have drawn increasing attention for their impact on system performance. With the continuous progress of integrated circuit technology, the system supply voltage has been continuously reduced while the functional density has been significantly improved. The minute noise interference at the output of the LDO may be coupled to sensitive circuit modules through the power network, triggering a chain reaction such as signal integrity degradation and measurement accuracy decline. Especially in application scenarios such as high-precision analog front-ends, radio frequency transceiver systems, and biomedical sensing, the noise level of the power rail is directly related to key indicators such as the signal-to-noise ratio and dynamic range of the system. For example, in the millimeter-wave radio frequency front-end of a 5G communication system, the high-frequency noise of the LDO may cause phase noise deterioration through local oscillator signal modulation; in an electroencephalogram signal acquisition system, the mixing of μV-level noise may lead to the submergence of weak physiological signals. Existing research shows that the noise spectral characteristics of the LDO (including components such as thermal noise, flicker noise, and switching noise) will penetrate into the load circuit through the frequency-domain attenuation characteristics of the power supply rejection ratio (PSRR), and this noise transfer mechanism is particularly prominent in the design of mixed-signal SoCs.

[0003] To obtain an LDO with lower output noise, especially low-frequency noise, a filter with a lower cut-off frequency is usually required, and such a filter has a large area. For the power supply of extremely sensitive circuits (VCO power supply), an independent LDO circuit is often required for separate power supply, thus restricting the area of the LDO from being too large. The area, power consumption, and noise are mutually contradictory, and it is difficult to remove low-frequency noise in a fully integrated chip. Summary of the Invention

[0004] Aiming at the above deficiencies in the prior art, the present invention provides a low-noise LDO circuit, which solves the problem of the mutual contradiction between the area, power consumption, and noise of the traditional LDO circuit.

[0005] To achieve the above invention objective, the technical solution adopted by the present invention is: a low-noise LDO circuit, including: a bandgap reference circuit, which improves the output reference voltage of the bandgap reference circuit by connecting the reverse-biased diodes in the triode in series.

[0006] Further: it also includes an error amplifier, a super source follower, a power device, a feedback resistor R1, and a feedback resistor R2;

[0007] The error amplifier is used to receive the output voltage of the low-noise LDO circuit and the reference voltage generated by the bandgap reference circuit, compare and amplify them, and obtain an error value;

[0008] The super source follower is used to control the gate voltage of the power device according to the change of the error value;

[0009] The power device is used to adjust the output current according to the gate voltage;

[0010] The feedback resistors R1 and R2 together form a feedback network, which is used to send the output voltage of the low-noise LDO circuit back to the error amplifier.

[0011] Furthermore: The input terminal of the bandgap reference circuit is connected to the first input terminal of the power device. The input terminal of the bandgap reference circuit also serves as the input terminal of the low-noise LDO circuit. The output terminal of the bandgap reference circuit is connected to the positive input terminal of the error amplifier. The negative input terminal of the error amplifier is respectively connected to one end of the feedback resistor R1 and the grounded feedback resistor R2. The other end of the feedback resistor R1, which is also the output terminal of the low-noise LDO circuit, is connected to the output terminal of the power device. The output terminal of the error amplifier is connected to the input terminal of the super source follower. The output terminal of the super source follower is connected to the second input terminal of the power device.

[0012] Furthermore: The bandgap reference circuit includes a field effect transistor M1. The gate of the field effect transistor M1 serves as the input terminal of the bandgap reference circuit. The drain of the field effect transistor M1 is respectively connected to the source of the field effect transistor M2 and the source of the field effect transistor M3. The drain of the field effect transistor M2 is respectively connected to the source of the field effect transistor M7 and the drain of the field effect transistor M9. The drain of the field effect transistor M7 is respectively connected to the drain of the field effect transistor M5, the gate of the field effect transistor M10, the gate of the field effect transistor M11, the gate of the field effect transistor M12, and the gate of the field effect transistor M13. The gate of the field effect transistor M5 is respectively connected to the gate of the field effect transistor M4, the drain of the field effect transistor M4, and the drain of the field effect transistor M6. The source of the field effect transistor M6 is respectively connected to the drain of the field effect transistor M3 and the drain of the field effect transistor M8. The source of the field effect transistor M8 and the source of the field effect transistor M9 are both grounded. The gate of the field effect transistor M6 and the gate of the field effect transistor M7 are connected. The gate of the field effect transistor M8 and the gate of the field effect transistor M9 are connected. The source of the field effect transistor M1, the source of the field effect transistor M4, and the source of the field effect transistor M5 are all connected to the same power supply voltage;

[0013] The sources of field effect transistors M10, M11, M12, and M13 are all connected to an external power supply as the input terminals of the bandgap reference circuit. The drain of field effect transistor M10 is connected to the emitter of transistor Q3. The emitter of transistor Q1 is respectively connected to the drain of field effect transistor M11, the gate of field effect transistor M2, and one end of resistor RD. The other end of resistor RD is connected to one end of resistor RE. The other end of resistor RE is connected to one end of resistor RF. The other end of resistor RF is respectively connected to the base of transistor Q3, the collector of transistor Q3, the collector of transistor Q1, the collector of transistor Q2, the collector of transistor Q4, and one end of resistor RC. The emitter of transistor Q2 is respectively connected to the gate of field effect transistor M3, the drain of field effect transistor M12, and one end of resistor RA. The other end of resistor RA is connected to one end of resistor RB. The other end of resistor RB is respectively connected to the other end of resistor RC and the base of transistor Q4. The emitter of transistor Q4 is respectively connected to the base of transistor Q2 and the drain of field effect transistor M13. The other end of resistor RA also serves as the output terminal of the bandgap reference circuit.

[0014] Further: Field effect transistors M1 to M9 form a folded cascode amplifier, field effect transistors M10 to M13 form a current mirror, transistors Q1 to Q4 are used to provide a negative temperature characteristic, resistor RC has a positive temperature coefficient, and resistors RA and RB have a negative temperature coefficient.

[0015] Further: The error amplifier is a folded cascode amplifier composed of field effect transistors.

[0016] The beneficial effects of the present invention are as follows:

[0017] 1. By connecting the reverse-biased diodes in series in the transistor, the output reference voltage of the bandgap reference circuit is increased.

[0018] 2. Based on the bandgap reference circuit structure with low noise that can output a relatively high voltage, the amplification factor of the reference voltage noise to the output terminal is reduced, enabling low-noise output across the entire frequency band without using a filter capacitor. Description of the Drawings

[0019] Figure 1 It is the bandgap reference circuit of the prior art solution.

[0020] Figure 2 It is a schematic diagram of a low-noise LDO circuit.

[0021] Figure 3 It is an example diagram of a low-noise LDO circuit. Detailed Embodiments

[0022] The specific embodiments of the present invention will be described below to facilitate those skilled in the art of the present technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art of the present technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions created using the concept of the present invention are within the scope of protection.

[0023] As Figure 1 shown, it is a bandgap reference circuit of the prior art solution, where the voltage across the resistor RC has a positive temperature characteristic, and the voltage difference V between the base and emitter of the triode has a negative temperature characteristic. By adjusting the resistance value, a voltage with zero temperature coefficient can be obtained. The output voltage V of the bandgap reference circuit is given by the weighted sum of the base voltage of the triode and V, so the amplification of the noise of the amplifier is almost zero. BE The output voltage V of the prior art is differentiated with respect to temperature T by the formula: REF is given by the weighted sum of the base voltage of the triode and V BE , so the amplification of the noise of the amplifier is almost zero.

[0024] The formula for differentiating the output voltage V of the prior art with respect to temperature T is: REF :

[0025]

[0026] where β is the amplification factor of the base current I of the triode b and the collector current I c ; N is the ratio of the number of triodes Q1 to the number of triodes Q2 in Figure 1 ; VT = (kT) / q, VT is the thermal voltage, and its physical meaning represents the characteristic voltage of a semiconductor device in thermal equilibrium and is directly related to temperature; V BE1 represents the voltage difference between the base and emitter of triode Q1, k is the Boltzmann constant, and q is the elementary charge.

[0027] At room temperature, the negative temperature coefficient of V BE is -1.5 mV / K, and the temperature coefficient of VT is +0.087 mV / k. Assuming N is equal to 24 and ignoring the resistance ratio of the first term in the formula, in order to obtain a voltage with zero temperature coefficient, it is deduced that RB / (RA + RB) is approximately equal to 0.185. The reverse bias voltage of the base-emitter junction of a general triode is 750 mV. Substituting into the formula, the output voltage V BE is only about 220 mV. If the reference level V in the LDO REF is lower, the feedback coefficient will be smaller, resulting in an increase in the amplification factor of the noise, and the output noise of the LDO will also increase accordingly. Therefore, the bandgap reference circuit of the prior art can only output a low-noise voltage V with a relatively small reference voltage REF with a lower reference level, the feedback coefficient will be smaller, resulting in an increase in the amplification factor of the noise, and the output noise of the LDO will also increase accordingly. Therefore, the bandgap reference circuit of the prior art can only output a low-noise voltage V with a relatively small reference voltage REFWhen the output voltage is fixed, the feedback coefficient becomes smaller, and the amplification factor of the reference voltage noise to the output end becomes larger, which is not good for the total LDO output noise.

[0028] In traditional designs, a low-pass filter circuit needs to be added to the output of the bandgap reference circuit to reduce noise output. The low-pass filter itself will also introduce noise. To achieve low-noise output in the entire frequency band, a low-pass filter with an extremely low cutoff frequency is required, and the area of the filter capacitor will be particularly large.

[0029] To solve the above-mentioned shortcomings, the present application provides a low-noise LDO circuit, including: a bandgap reference circuit, wherein the output reference voltage of the bandgap reference circuit is increased by connecting reverse-biased diodes in a triode in series.

[0030] like Figure 2 As shown, the low noise LDO circuit provided by the present application also includes an error amplifier, a super source follower, a power device, a feedback resistor R1 and a feedback resistor R2;

[0031] The error amplifier is used to receive the output voltage of the low-noise LDO circuit and the reference voltage generated by the bandgap reference circuit, and compare and amplify them to obtain an error value;

[0032] The super source follower is used to control the gate voltage of the power device according to the change of the error value;

[0033] The power device is used to regulate the output current according to the gate voltage;

[0034] Feedback resistor R1 and feedback resistor R2 together form a feedback network for sending the output voltage of the low noise LDO circuit back to the error amplifier.

[0035] Specifically, the input end of the bandgap reference circuit is connected to the first input end of the power device, the input end of the bandgap reference circuit also serves as the input end of the low-noise LDO circuit, the output end of the bandgap reference circuit is connected to the positive input end of the error amplifier, the negative input end of the error amplifier is respectively connected to one end of the feedback resistor R1 and the grounded feedback resistor R2, the other end of the feedback resistor R1 is also connected to the output end of the power device as the output end of the low-noise LDO circuit, the output end of the error amplifier is connected to the input end of the super source follower, and the output end of the super source follower is connected to the second input end of the power device.

[0036] In order to obtain lower output noise in the full frequency range, the noise of the bandgap reference circuit needs to be very low and the noise of the bandgap reference circuit should account for a small proportion of the output noise. The output reference voltage V REF The transistor base and V BE The weighted sum of the amplifiers achieves zero temperature coefficient and the amplifier noise is reduced to V REFThe magnification factor is almost zero, thus achieving low noise; moreover, since the noise output by the bandgap reference circuit is very small, a low-pass filter is not required, greatly reducing the circuit area. Since the output voltage of the bandgap reference circuit is higher than the output voltage of the existing low-noise technology, when the output voltage is fixed, the feedback coefficient increases, and the magnification factor of the noise of the reference voltage to the output end becomes smaller. The output noise of the bandgap reference circuit accounts for a smaller proportion of the total noise of the LDO, thereby reducing the output noise.

[0037] As Figure 3 shown, in an embodiment of the present invention, the bandgap reference circuit includes a field-effect transistor M1. The gate of the field-effect transistor M1 serves as the input end of the bandgap reference circuit. The drain of the field-effect transistor M1 is respectively connected to the source of the field-effect transistor M2 and the source of the field-effect transistor M3. The drain of the field-effect transistor M2 is respectively connected to the source of the field-effect transistor M7 and the drain of the field-effect transistor M9. The drain of the field-effect transistor M7 is respectively connected to the drain of the field-effect transistor M5, the gate of the field-effect transistor M10, the gate of the field-effect transistor M11, the gate of the field-effect transistor M12, and the gate of the field-effect transistor M13. The gate of the field-effect transistor M5 is respectively connected to the gate of the field-effect transistor M4, the drain of the field-effect transistor M4, and the drain of the field-effect transistor M6. The source of the field-effect transistor M6 is respectively connected to the drain of the field-effect transistor M3 and the drain of the field-effect transistor M8. The sources of the field-effect transistor M8 and the field-effect transistor M9 are both grounded. The gate of the field-effect transistor M6 is connected to the gate of the field-effect transistor M7. The gate of the field-effect transistor M8 is connected to the gate of the field-effect transistor M9. The sources of the field-effect transistor M1, the field-effect transistor M4, and the field-effect transistor M5 are all connected to the same power supply voltage.

[0038] The sources of the field-effect transistor M10, the field-effect transistor M11, the field-effect transistor M12, and the field-effect transistor M13 all serve as the input ends of the bandgap reference circuit and are connected to an external power supply. The drain of the field-effect transistor M10 is connected to the emitter of the triode Q3. The emitter of the triode Q1 is respectively connected to the drain of the field-effect transistor M11, the gate of the field-effect transistor M2, and one end of the resistor RD. The other end of the resistor RD is connected to one end of the resistor RE. The other end of the resistor RE is connected to one end of the resistor RF. The other end of the resistor RF is respectively connected to the base of the triode Q3, the collector of the triode Q3, the collector of the triode Q1, the collector of the triode Q2, the collector of the triode Q4, and one end of the resistor RC. The emitter of the triode Q2 is respectively connected to the gate of the field-effect transistor M3, the drain of the field-effect transistor M12, and one end of the resistor RA. The other end of the resistor RA is connected to one end of the resistor RB. The other end of the resistor RB is respectively connected to the other end of the resistor RC and the base of the triode Q4. The emitter of the triode Q4 is respectively connected to the base of the triode Q2 and the drain of the field-effect transistor M13. The other end of the resistor RA also serves as the output end of the bandgap reference circuit.

[0039] Specifically, field effect transistors M1 to M9 form a folded cascode amplifier, field effect transistors M10 to M13 form a current mirror, transistors Q1 to Q4 are used to provide negative temperature characteristics, resistor RC has a positive temperature coefficient, and resistors RA and RB have negative temperature coefficients.

[0040] Specifically, the error amplifier is a folded cascode amplifier composed of field effect transistors. In this embodiment, the error amplifier includes field effect transistor M15. The gate of field effect transistor M15 is connected to the other end of resistor RA. The emitter of field effect transistor M15 is respectively connected to the emitter of field effect transistor M16 and the drain of field effect transistor M14. The drain of field effect transistor M15 is respectively connected to the emitter of field effect transistor M22 and the drain of field effect transistor M24. The gate of field effect transistor M16 serves as the negative input terminal of the error amplifier. The drain of field effect transistor M16 is respectively connected to the emitter of field effect transistor M21 and the drain of field effect transistor M23. The drain of field effect transistor M21 is respectively connected to the drain of field effect transistor M19, the gate of field effect transistor M17, and the gate of field effect transistor M18. The emitter of field effect transistor M19 is connected to the drain of field effect transistor M17. The drain of field effect transistor M22 is connected to the drain of field effect transistor M20. The source of field effect transistor M20 is connected to the drain of field effect transistor M18. The gate of field effect transistor M20 is connected to the gate of field effect transistor M19. The gate of field effect transistor M21 is connected to the gate of field effect transistor M22. The gate of field effect transistor M23 is connected to the gate of field effect transistor M24. The drain of field effect transistor M22 also serves as the output terminal of the error amplifier.

[0041] Preferably, as Figure 3 shown, the source of field effect transistor M14, the source of field effect transistor M17, and the source of field effect transistor M18 can also be connected to the source of field effect transistor M13, that is, the error amplifier and the bandgap reference circuit use the same external power supply input.

[0042] In this embodiment, the super source follower (SSF, Super Source Follower) includes field effect transistor M26. The gate of field effect transistor M26 serves as the input terminal of the super source follower and is connected to the output terminal of the error amplifier (i.e., the drain of field effect transistor M22). The drain of field effect transistor M26 is respectively connected to the emitter of field effect transistor M25 and the drain of field effect transistor M28. The emitter of field effect transistor M26 is respectively connected to the drain of field effect transistor M27 and the gate of field effect transistor M28. The drain of field effect transistor M28 also serves as the output terminal of the super source follower and is connected to the power device.

[0043] In this embodiment, a field effect transistor M29 is used to equivalently represent a power device. The gate of the field effect transistor M29 serves as the second input terminal of the power device and is connected to the drain of the field effect transistor M28. The drain of the field effect transistor M29 serves as the first input terminal of the rate device and is connected to the source of the field effect transistor M13. The source of the field effect transistor M29 serves as the output terminal of the power device.

[0044] Optionally, the output terminal of the low-noise LDO circuit can be connected to an error amplifier. As in this embodiment, the other end of the feedback resistor R1 serves as the output terminal of the low-noise LDO circuit and is also connected to one end of the capacitor C1. The other end of the capacitor C1 is connected to the drain of the field effect transistor M24.

[0045] The beneficial effect of connecting the output terminal of the low-noise LDO circuit to the drain of the field effect transistor M24 through the capacitor C1 is as follows: By using the cascode compensation technique, the output pole is pushed to a higher frequency, making the entire circuit stable and preventing the problem of output oscillation. This cascode compensation has no feedforward path theoretically compared with the traditional Miller compensation.

[0046] In summary, without using a large-area low-pass filter, the present invention adopts a high-output reference voltage and a low-noise bandgap reference circuit, and finally realizes the reduction of the output noise of the LDO in the full frequency band. It greatly alleviates the contradiction between area and noise, and realizes a fully integrated full-band low-noise LDO.

[0047] The above embodiments are only used to illustrate the technical solutions of the present application, not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A low-noise LDO circuit, comprising: Bandgap reference circuit, error amplifier, super source follower, power device, feedback resistor R1 and feedback resistor R2; The bandgap reference circuit increases the output reference voltage of the bandgap reference circuit by connecting reverse-biased diodes in series in a triode. The error amplifier is used to receive the output voltage of the low-noise LDO circuit and the reference voltage generated by the bandgap reference circuit, compare and amplify them, and obtain an error value; The super source follower is used to control the gate voltage of the power device according to the change of the error value; the power device is used to adjust the output current according to the gate voltage; the feedback resistors R1 and R2 together form a feedback network, which is used to send the output voltage of the low-noise LDO circuit back to the error amplifier. The input terminal of the bandgap reference circuit is connected to the first input terminal of the power device. The input terminal of the bandgap reference circuit also serves as the input terminal of the low-noise LDO circuit. The output terminal of the bandgap reference circuit is connected to the positive input terminal of the error amplifier. The negative input terminal of the error amplifier is respectively connected to one end of the feedback resistor R1 and the grounded feedback resistor R2. The other end of the feedback resistor R1 serves as the output terminal of the low-noise LDO circuit and is also connected to the output terminal of the power device. The output terminal of the error amplifier is connected to the input terminal of the super source follower. The output terminal of the super source follower is connected to the second input terminal of the power device. It is characterized in that the bandgap reference circuit includes a field effect transistor M1. The gate of the field effect transistor M1 serves as the input terminal of the bandgap reference circuit. The drain of the field effect transistor M1 is respectively connected to the source of the field effect transistor M2 and the source of the field effect transistor M3. The drain of the field effect transistor M2 is respectively connected to the source of the field effect transistor M7 and the drain of the field effect transistor M9. The drain of the field effect transistor M7 is respectively connected to the drain of the field effect transistor M5, the gate of the field effect transistor M10, the gate of the field effect transistor M11, the gate of the field effect transistor M12, and the gate of the field effect transistor M13. The gate of the field effect transistor M5 is respectively connected to the gate of the field effect transistor M4, the drain of the field effect transistor M4, and the drain of the field effect transistor M6. The source of the field effect transistor M6 is respectively connected to the drain of the field effect transistor M3 and the drain of the field effect transistor M8. The source of the field effect transistor M8 and the source of the field effect transistor M9 are both grounded. The gate of the field effect transistor M6 and the gate of the field effect transistor M7 are connected. The gate of the field effect transistor M8 and the gate of the field effect transistor M9 are connected; the source of the field effect transistor M1, the source of the field effect transistor M4, and the source of the field effect transistor M5 are all connected to the same power supply voltage; The sources of field effect transistors M10, M11, M12, and M13 are all connected to an external power supply as the input terminals of the bandgap reference circuit. The drain of field effect transistor M10 is connected to the emitter of transistor Q3. The emitter of transistor Q1 is respectively connected to the drain of field effect transistor M11, the gate of field effect transistor M2, and one end of resistor RD. The other end of resistor RD is connected to one end of resistor RE. The other end of resistor RE is connected to one end of resistor RF. The other end of resistor RF is respectively connected to the base of transistor Q3, the collector of transistor Q3, the collector of transistor Q1, the collector of transistor Q2, the collector of transistor Q4, and one end of resistor RC. The emitter of transistor Q2 is respectively connected to the gate of field effect transistor M3, the drain of field effect transistor M12, and one end of resistor RA. The other end of resistor RA is connected to one end of resistor RB. The other end of resistor RB is respectively connected to the other end of resistor RC and the base of transistor Q4. The emitter of transistor Q4 is respectively connected to the base of transistor Q2 and the drain of field effect transistor M13. The other end of resistor RA also serves as the output terminal of the bandgap reference circuit.

2. The low-noise LDO circuit according to claim 1, wherein Field effect transistors M1 to M9 form a folded cascode amplifier, field effect transistors M10 to M13 form a current mirror, transistors Q1 to Q4 are used to provide negative temperature characteristics, the voltage drop across resistor RC has a positive temperature coefficient, and the voltage drops across resistors RA and RB have negative temperature coefficients.

3. The low-noise LDO circuit according to claim 1, wherein, The error amplifier is a folded cascode amplifier composed of field effect transistors.

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