CN106200745A - A kind of low noise direct voltage source - Google Patents

Abstract

The invention discloses a low-noise DC voltage source, which includes a series-connected stabilized voltage source and an LC network, and is characterized in that it also includes a feed-forward compensation network connected in parallel with the LC network, and the feed-forward compensation network belongs to the noise of the stabilized voltage source in the The output is added inversely with the original noise. The present invention reduces the noise through the LC network, and can stabilize the circuit voltage at the same time; secondly, the feedforward compensation network is used to reverse the phase of the noise of the voltage regulator, and then add it to the noise of the voltage regulator at the output end to further reduce the noise of the power supply .

Description

A Low Noise DC Voltage Source

technical field

The invention relates to a low-noise DC voltage source, belonging to the field of noise reduction of DC voltage sources.

Background technique

In today's society, people greatly enjoy the convenience brought by electronic equipment, but most electronic equipment needs DC power, and basically all electronic products are powered by voltage stabilizers. Moreover, small precision electronic facilities also require a very pure power supply with as little ripple and noise as possible to avoid adverse effects on the normal operation of electronic equipment. Very low noise voltage and current sources are often part of a low frequency noise measurement system. In particular, these voltage or current sources are used to bias test equipment that must have very low noise levels in the background noise system. Especially for some sensitive electronic devices, the requirements for noise are very high, and the introduction of power supply noise will increase the noise in the entire circuit. In precision instruments, radar and other systems, it is necessary to provide extremely low-noise power supply voltage or bias voltage for low-noise microwave amplifiers, electro-optic modulators and photodetectors, so as to reduce the coupling of voltage noise to signal noise and improve the accuracy of the circuit. degree. All countries in the world attach great importance to the research on low-noise regulated voltage sources. However, the noise voltage (DC to 40kHz) of commonly used commercially available voltage regulator chips (such as LM2940) is generally -125 ~ -130dBV/sqrt (Hz), which cannot meet the requirements of high-performance systems.

The predecessors have made some efforts in this regard. In the past design and implementation of very low noise voltage or current sources, some of the aforementioned defects can be reduced, but combined with the feedforward method, the performance achieved can be further optimized. , to obtain a voltage source with better performance, which is a very important improvement in performance for circuit design using DC power supplies, especially for circuits with relatively high noise requirements. Therefore, the main content of this article is to design a low-noise voltage source circuit with superior performance, and to measure and analyze its data, in order to achieve the purpose of making the designed circuit applicable to practice.

Contents of the invention

Purpose of the invention: The present invention proposes a low-noise DC voltage source, which reduces the noise of the DC voltage source, and has a simple structure and high cost performance.

Technical solution: The technical solution adopted in the present invention is a low-noise DC voltage source, which includes a series-connected voltage regulator and an LC network, and also includes a feedforward compensation network connected in parallel with the LC network. The noise cancels the original noise at the output.

Preferably, the feedforward compensation network is a subtractor. The subtractor includes a first capacitor, and a proportional subtractor composed of an operational amplifier, a first resistor, and a second resistor;

One end of the first capacitor is connected to the input end of the LC network, and the other end is connected to an input end of the operational amplifier, and the output end of the operational amplifier is also output to the load and connected to the output end of the LC network.

Preferably, the LC network includes a second capacitor, a first inductor and a third capacitor, wherein one end of the second capacitor is grounded and the other end is connected to the first inductor;

The other end of the first inductor is connected to the third capacitor, and the other end of the third capacitor is grounded.

Preferably, the voltage stabilizing source is an LM2940 chip.

Beneficial effects: the present invention reduces the noise through the LC network, and can stabilize the circuit voltage at the same time; secondly, the noise of the voltage stabilization source is reversed by using the feedforward compensation network, and then added to the noise of the voltage stabilization source at the output end, further Reduce power supply noise. According to the simulation experiment, it can be found that adopting the feed-forward voltage source can reduce the noise of the commonly used commercially available voltage regulator chips by about 20dB, so the present invention has high practical and research value.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 is a circuit topology diagram of the present invention.

detailed description

Below in conjunction with accompanying drawing and specific embodiment, further illustrate the present invention, should be understood that these embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention, after having read the present invention, those skilled in the art will understand various aspects of the present invention Modifications in equivalent forms all fall within the scope defined by the appended claims of this application.

As shown in Fig. 1, the low-noise DC voltage source of the present invention includes three parts, namely a voltage stabilizer, an LC network and a feed-forward compensation network.

As shown in Figure 2, the voltage regulator source is a voltage regulator chip U3. The external voltage VCC provides power to the voltage regulator chip U3. Voltage regulator chip U3 uses LM2940 chip. The input voltage u _i is input into the voltage stabilizing chip U3, and then the voltage stabilizing chip U3 outputs the first DC voltage. The first DC voltage at this time contains a lot of noise, and according to the simulation results, the noise power of the first DC voltage at around 40KHz is about -110dB.

The LC network includes a second capacitor C2, a first inductor L1 and a third capacitor C3, wherein one end of the second capacitor C2 is grounded and the other end is connected to the first inductor L1. The other end of the first inductor L1 is connected to the third capacitor C3, and the other end of the third capacitor C3 is grounded. The second capacitor C2 is 10nF, the third capacitor C3 is 10nF, and the first inductor L1 is 100uH. The first DC voltage output by the voltage stabilizing chip U3 is applied to the common node of the second capacitor C2 and the first inductor L1, and the common node of the second capacitor C2 and the first inductor L1 serves as an input terminal of the LC network. The common node of the third capacitor C3 and the first inductor L1 is output to the load as the output terminal of the LC network. The second capacitor C2 and the third capacitor C3 function to stabilize the voltage. When the voltage is unstable, they can be temporarily used as discharge capacitors to make the voltage more stable. The first inductor L1 functions to pass DC and block AC.

The feedforward compensation network includes a first capacitor C1, and a proportional subtractor composed of an operational amplifier U1, a first resistor R1, and a second resistor R2. Wherein, one end of the first capacitor C1 is connected to the input end of the LC network, and the other end is connected to an input end of the operational amplifier. The output of the operational amplifier is also output to the load and connected to the output of the LC network. The first capacitor C1 is 10nF, the first resistor R1 is 40kΩ, and the second resistor R2 is 10kΩ.

The feedforward compensation network is connected in parallel with the LC network, and the first DC voltage and its noise are simultaneously input into the LC network and the feedforward compensation network, while the feedforward compensation network and the LC network simultaneously output the noise to the load. Since the feed-forward compensation network is a subtractor, the noise output by the LC network is opposite to the noise output by the feed-forward compensation network, and the anti-phase addition at the load cancels each other.

Connected by the circuit and according to Ohm's law and Kirchhoff's law:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}$

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; w</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; w</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}$

In the above formula, I _c1 is the current flowing through the second resistor R2, continuing we can obtain the transfer function of the LC network as

$\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; w</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; w</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}$

In the above formula, u _o is the output voltage of the low-noise DC voltage source, and u _i is the input voltage of the low-noise DC voltage source.

Finally, the noise-compensated first DC voltage is amplified by the second amplifier A2 with a voltage gain of 10v/v to become the output voltage u _o .

The measurement results of specific noise can be obtained through circuit simulation. We can find that compared with the noise of -125dB commonly used voltage regulator chips on the market. After the noise compensation of the feed-forward compensation network in the present invention, the output noise is obviously reduced, and the noise is only about -158dB at 40kHz, and the noise reduction is about 20dB.

Claims (5)

1. A low-noise direct current voltage source, comprising a series voltage regulator and an LC network, is characterized in that: it also includes a feedforward compensation network connected in parallel with the LC network, and the feedforward compensation network of the subordinate feedforward compensation network puts the noise of the voltage regulator at the output terminal Inverted and added to the original noise. 2. The low-noise DC voltage source according to claim 1, wherein the feed-forward compensation network is a subtractor. 3. The low-noise DC voltage source according to claim 2, characterized in that: said subtractor comprises a first capacitor (C1), and is made up of an operational amplifier, a first resistor (R1), and a second resistor (R2). The proportional subtractor; One end of the first capacitor (C1) is connected to the input end of the LC network, and the other end is connected to an input end of the operational amplifier, and the output end of the operational amplifier is also output to the load and connected to the output end of the LC network. 4. The low-noise DC voltage source according to claim 1, characterized in that: said LC network comprises a second capacitor (C2), a first inductor (L1) and a third capacitor (C3), wherein the second capacitor ( C2) one end is grounded, and the other end is connected to the first inductor (L1); The other end of the first inductor (L1) is connected to the third capacitor (C3), and the other end of the third capacitor (C3) is grounded. 5. The low-noise DC voltage source according to claim 1, characterized in that: the voltage stabilizing source is an LM2940 chip.