A single power rail-to-rail absolute value circuit

Abstract

A single power rail-to-rail absolute value circuit, comprising: a positive half-cycle signal processing circuit, the positive half-cycle signal processing circuit comprising a first resistor and a positive signal elimination device, the first end of the first resistor is connected to the input signal end; a negative half-cycle signal processing circuit, the negative half-cycle signal processing circuit comprising a second resistor and a negative signal elimination device, the first end of the second resistor is connected to the input signal end; an absolute value operation processing circuit, the absolute value operation processing circuit comprising a first operational amplifier, the in-phase input end of the first operational amplifier is connected to the output end of the negative half-cycle signal processing circuit, and the inverting input end of the first operational amplifier is connected to the output end of the positive half-cycle signal processing circuit. The single power rail-to-rail absolute value circuit structure of the present invention is cleverly designed, which improves the measurement accuracy of the absolute value voltage and reduces the product cost.

Description

Technical Field

[0001] The present invention relates to the field of absolute value circuits, and more particularly to a single power supply rail-to-rail absolute value circuit. Background Art

[0002] Most absolute value circuits use positive and negative dual power supplies. Common absolute value circuits include Figure 1 In fact, in many practical applications, due to cost or other practical conditions (such as space), there is no dual power supply condition, and it can only work under a single positive power supply condition (negative power supply is rarely used).

[0003] In order to achieve the purpose of inverting the voltage waveform from the negative half cycle to the positive half cycle in the circuit, a diode is often used to achieve this goal. Due to the forward voltage drop of the diode and the nonlinear characteristics of the PN junction, the actual voltage waveform obtained is distorted, which will cause large measurement errors when precise measurements are required, especially when measuring small signals, such as Figure 1 The diodes D1 and D2, especially D2, are affected.

[0004] The Chinese invention patent No. 92108452.8 provides an improved absolute value circuit, which uses a single power supply scheme for absolute value measurement without using a diode. The principle is: when a negative polarity signal is input, the op amp amplifies inversely and outputs a positive signal, which is synthesized with the negative half cycle of the original signal after resistor voltage division to output a positive half cycle signal; when a positive polarity signal is input, the op amp is clamped to 0V due to the grounding of the negative pole of the power supply, and the signal output is obtained by voltage division of the original signal to obtain a positive half cycle, thereby achieving the purpose of measuring the absolute value of the signal. The defects of this scheme are also obvious: 1) The input range of the negative half cycle of the signal exceeds the negative power supply range of the op amp. Even if the op amp can work, it is usually not recommended unless a relatively expensive special op amp is used, such as: AD8277 and other similar op amps; 2) The impedance of the voltage divider circuit is large, and the input impedance of the subsequent circuit is required to be large when used, otherwise the measurement error cannot be ignored.

[0005] The utility model patent No. 200420091345.4 proposes a "wideband low error absolute value circuit", which is said to be able to work under single power supply conditions. In fact, similar problems exist, and the main reason is that the input voltage exceeds the allowable range of the negative power supply. Figure 2 As shown in the figure, it is the output waveform diagram when a single-power op amp is used to amplify the sine wave in phase. The dotted line is the input signal waveform, and the solid line is the output waveform. It can be seen from the figure that when the signal is in the negative half cycle, the output waveform has been saturated and the circuit is in an abnormal working state. Figure 2As shown in the figure, the dotted line shows the input signal waveform. In the conventional absolute value operation circuit, since a diode is used as a switching device, a forward voltage drop will inevitably occur, and the actual waveform obtained will be distorted, resulting in measurement errors, especially for small signals.

[0006] The Chinese invention patent No. 201710348164.7 provides a "distortion-free absolute value circuit composed of an ordinary operational amplifier". It does not use diodes but uses transistors as switches. It is a good circuit design solution. However, the circuit cannot work under single power supply conditions.

[0007] Usually, conventional op amps will have conditional restrictions when they are designed, that is, the input voltage Vi cannot exceed the positive and negative power supplies, otherwise, the circuit will malfunction. Experiments show that for a +5V power supply signal, if an LM324 op amp is used, when the input signal is 1.5Vrms, the output saturation phenomenon will occur in the corresponding negative half-cycle signal. When it is less than this value, it will perform normally, and the negative half-cycle output signal is 0V, indicating that the op amp has a certain "absorption" ability for small negative signals. Obviously, when the op amp negative power supply is grounded, the input voltage of the negative half cycle can easily exceed this restriction. Therefore, such a design is not practical and has no practical significance.

[0008] Rail-to-rail operational amplifiers are of great significance in practical applications. Under the same conditions, the effective range of the A / D converter can usually be fully utilized to improve the measurement accuracy. Therefore, the application of single-power supply operational amplifier absolute value circuits to rail-to-rail operational amplifiers is of great practical significance. Summary of the invention

[0009] The object of the present invention is to provide a single power supply rail-to-rail absolute value circuit.

[0010] The present invention aims to solve the problems of the above-mentioned traditional absolute value circuit.

[0011] Compared with the prior art, the technical solution of the present invention and its beneficial effects are as follows:

[0012] A single-power rail-to-rail absolute value circuit comprises: a positive half-cycle signal processing circuit, the positive half-cycle signal processing circuit comprises a first resistor and a positive signal elimination device, the first end of the first resistor is connected to an input signal end, the first end of the positive signal elimination device is connected to the second end of the first resistor, and the second end of the positive signal elimination device is grounded; a negative half-cycle signal processing circuit, the negative half-cycle signal processing circuit comprises a second resistor and a negative signal elimination device, the first end of the second resistor is connected to the input signal end, the first end of the negative signal elimination device is connected to the second end of the second resistor, and the second end of the negative signal elimination device is grounded; an absolute value operation processing circuit, the absolute value operation processing circuit comprises a first operational amplifier, the in-phase input end of the first operational amplifier is connected to the output end of the negative half-cycle signal processing circuit, and the inverting input end of the first operational amplifier is connected to the output end of the positive half-cycle signal processing circuit.

[0013] As a further improvement, the positive signal elimination device and the negative signal elimination device are both diodes; the positive electrode of the positive signal elimination device is connected to the second end of the first resistor, and the negative electrode of the positive signal elimination device is grounded; the positive electrode of the negative signal elimination device is grounded, and the negative electrode of the negative signal elimination device is connected to the second end of the second resistor.

[0014] As a further improvement, it also includes a signal adjustment circuit, which includes: a third resistor, a first end of the third resistor is connected to the second end of the second resistor, the first end of the third resistor is connected to the negative electrode of the positive signal elimination device, and the second end of the third resistor is connected to the non-inverting input terminal of the first operational amplifier; a fourth resistor, a first end of the fourth resistor is connected to the second end of the third resistor, the first end of the fourth resistor is connected to the non-inverting input terminal of the first operational amplifier, and the second end of the fourth resistor is grounded.

[0015] As a further improvement, the absolute value operation processing circuit also includes: a fifth resistor, a first end of the fifth resistor is connected to the second end of the first resistor, the first end of the fifth resistor is connected to the positive electrode of the negative signal elimination device, and the second end of the fifth resistor is connected to the inverting input terminal of the first operational amplifier; a sixth resistor, a first end of the sixth resistor is connected to the second end of the fifth resistor, the first end of the sixth resistor is connected to the inverting input terminal of the first operational amplifier, and the second end of the sixth resistor is connected to the output terminal of the first operational amplifier.

[0016] As a further improvement, it also includes a signal follower circuit, which includes a second operational amplifier, the second end of the third resistor is connected to the non-inverting input terminal of the second operational amplifier, the first end of the fourth resistor is connected to the non-inverting input terminal of the second operational amplifier, the inverting input terminal of the second operational amplifier is connected to the output terminal of the second operational amplifier, and the output terminal of the second operational amplifier is connected to the non-inverting input terminal of the first operational amplifier.

[0017] As a further improvement, the signal follower circuit also includes: a seventh resistor, a first end of the seventh resistor is connected to the output end of the second operational amplifier, and a second end of the seventh resistor is connected to the non-inverting input end of the first operational amplifier; a first capacitor, one end of the first capacitor is connected to the positive power supply of the second operational amplifier, and the other end of the first capacitor is grounded.

[0018] As a further improvement, the model of the first operational amplifier is SGM8054.

[0019] As a further improvement, the model of the second operational amplifier is SGM8054.

[0020] As a further improvement, the positive signal elimination device and the negative signal elimination device are both Schottky diodes.

[0021] The beneficial effects of the present invention are as follows: the present invention adopts a common rail-to-rail operational amplifier, cooperates with a resistor and a Schottky diode to use a single power supply to form an absolute value circuit, the circuit is simple, the logic is clear, and it is easy to adjust. On the one hand, it solves the problem that the absolute value voltage cannot be measured with high precision due to the forward voltage drop when using a rectifier diode. On the other hand, the circuit uses a single power supply rail-to-rail to work, which not only simplifies the design, improves the measurement accuracy, and reduces the product cost, but also saves space, so it is of great practical significance in practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a common absolute value circuit diagram provided by the background technology of the present invention.

[0023] Figure 2 It is an output waveform diagram of the background technology of the present invention when a single-power operational amplifier is used to amplify a sine wave in phase.

[0024] Figure 3 It is a structural block diagram of a single-power rail-to-rail absolute value circuit provided in Embodiment 1 of the present invention.

[0025] Figure 4 It is a single power rail-to-rail absolute value circuit diagram provided by Embodiment 1 of the present invention.

[0026] Figure 5It is a single power rail-to-rail absolute value circuit diagram provided by the second embodiment of the present invention.

[0027] In the figure: 1. Positive half-cycle signal processing circuit 2. Negative half-cycle signal processing circuit

[0028] 3. Absolute value operation processing circuit 4. Signal adjustment circuit 5. Signal following circuit DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0030] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0031] Reference Figure 3 to Figure 4As shown, a single power rail-to-rail absolute value circuit includes: a positive half-cycle signal processing circuit 1, the positive half-cycle signal processing circuit 1 includes a first resistor R5 and a positive signal elimination device D2, the first end of the first resistor R5 is connected to the input signal end, the first end of the positive signal elimination device D2 is connected to the second end of the first resistor R5, and the second end of the positive signal elimination device D2 is grounded; a negative half-cycle signal processing circuit 2, the negative half-cycle signal processing circuit 2 includes a second resistor R1 and a negative signal elimination device D1, the first end of the second resistor R1 is also connected to the input signal end, the first end of the negative signal elimination device D1 is connected to the second end of the second resistor R1, and the second end of the negative signal elimination device D1 is grounded; an absolute value operation processing circuit 3, the absolute value operation processing circuit 3 includes a first operational amplifier U1B, the inverting input end of the first operational amplifier U1B is connected to the output end of the positive half-cycle signal processing circuit 1; a signal adjustment circuit 4, the first end of the signal adjustment circuit 4 is connected to the output end of the negative half-cycle signal processing circuit 2, and the second end of the signal adjustment circuit 4 is connected to the non-inverting input end of the first operational amplifier U1B. The single-power supply absolute value circuit of the present invention adopts a single power supply, reduces the types of power supplies, saves space and reduces costs; the present invention does not use ordinary diodes as commutation elements, reduces measurement errors to the maximum extent and improves measurement accuracy; the present invention adopts ordinary rail-to-rail operational amplifiers, does not need to use expensive special ICs, makes maximum use of the A / D converter range and also improves signal measurement accuracy; the circuit topology logic of the present invention is clear, the circuit adjustment is simple, and it is easy to use, which has great practical significance.

[0032] Reference Figure 4 As shown, the positive signal elimination device D2 and the negative signal elimination device D1 are both diodes; the positive electrode of the positive signal elimination device D2 is connected to the second end of the first resistor R5, and the negative electrode of the positive signal elimination device D2 is grounded; the positive electrode of the negative signal elimination device D1 is grounded, and the negative electrode of the negative signal elimination device D1 is connected to the second end of the second resistor R1.

[0033] Reference Figure 4 As shown, a single-power rail-to-rail absolute value circuit also includes a signal adjustment circuit 4, which includes: a third resistor R2, a first end of the third resistor R2 is connected to the second end of the second resistor R1, and a first end of the third resistor R2 is connected to the negative electrode of the positive signal elimination device D2; a fourth resistor R3, a first end of the fourth resistor R3 is connected to the second end of the third resistor R2, and a second end of the fourth resistor R3 is grounded.

[0034] Reference Figure 4As shown, the absolute value operation processing circuit 3 also includes: a fifth resistor R6, the first end of the fifth resistor R6 is connected to the second end of the first resistor R5, the first end of the fifth resistor R6 is connected to the positive electrode of the positive signal elimination device D2, and the second end of the fifth resistor R6 is connected to the inverting input end of the first operational amplifier U1B; a sixth resistor R7, the first end of the sixth resistor R7 is connected to the second end of the fifth resistor R6, the first end of the sixth resistor R7 is connected to the inverting input end of the first operational amplifier U1B, and the second end of the sixth resistor R7 is connected to the output end of the first operational amplifier U1B. The fifth resistor R6 and the sixth resistor R7 have the same resistance value.

[0035] Reference Figure 4 As shown, a single-power rail-to-rail absolute value circuit also includes a signal follower circuit 5, wherein the signal follower circuit 5 includes a second operational amplifier U1A, the second end of the third resistor R2 is connected to the non-inverting input end of the second operational amplifier U1A, the first end of the fourth resistor R3 is connected to the non-inverting input end of the second operational amplifier U1A, the inverting input end of the second operational amplifier U1A is connected to the output end of the second operational amplifier U1A, and the output end of the second operational amplifier U1A is connected to the non-inverting input end of the first operational amplifier U1B.

[0036] Reference Figure 4 As shown, the signal follower circuit 5 also includes: a seventh resistor R4, a first end of the seventh resistor R4 is connected to the output end of the second operational amplifier U1A, and a second end of the seventh resistor R4 is connected to the non-inverting input end of the first operational amplifier U1B; a first capacitor C1, one end of the first capacitor C1 is connected to the positive power supply of the second operational amplifier U1A, and the other end of the first capacitor C1 is grounded.

[0037] Reference Figure 4 As shown, the model of the first operational amplifier U1B is SGM8054.

[0038] Reference Figure 4 As shown, the model of the second operational amplifier U1A is SGM8054.

[0039] Reference Figure 4 As shown, the positive signal elimination device D2 and the negative signal elimination device D1 are both Schottky diodes.

[0040] Reference Figure 3As shown, a principle block diagram of a single-power supply distortion-free absolute value circuit composed of an ordinary rail-to-rail operational amplifier of the present invention is given. Its working principle is: the input signal is simultaneously sent to the "negative signal processing at the same phase end" and the "positive signal processing at the opposite phase end" links for signal preprocessing to eliminate the "negative half-cycle" and "positive half-cycle" signals that affect the operation of the operational amplifier, that is: the inverting input end of the operational amplifier is "afraid" of positive signals, so the positive signal is eliminated at the inverting input end, and the inverting input end is "afraid" of negative signals, so the negative signal is eliminated at the same phase input end, and then the signals are synthesized, and the output signal becomes the absolute value of the input signal.

[0041] The working principle of a single power rail-to-rail absolute value circuit provided in this embodiment is:

[0042] The input signal Vi is connected to the inverting input path of the resistor R5 at the upper end. The resistor R5 and the Schottky diode D2 form a positive half-cycle signal processing circuit 1. D2 uses a Schottky diode with a low forward voltage drop. The forward voltage drop is only 0.2~0.3V when the current is about 1mA. In this way, the voltage UB will be clamped at +0.2~0.3V in the positive half cycle of the signal, and in the negative half cycle of the signal, D2 is reverse biased and does not work, so the UB voltage value is not affected. For the voltage UB, when the signal is negative, an inverting amplifier is formed by resistors R6, R7, and op amp U1B, and the output signal Vo is positive. Because the positive voltage of UB is only 0.2~0.3V, the op amp cannot output a negative voltage, and it is easy to clamp the signal at 0V, thereby converting the negative half-cycle signal into a positive half-cycle output;

[0043] Input signal Vi, the lower end is connected to the in-phase input path of resistor R1. Resistor R1 and Schottky diode D1 form negative half-cycle signal processing circuit 2. Like D2, D1 also uses a Schottky diode with a lower forward voltage drop. The voltage UA will be clamped at -0.2~-0.3V in the negative half cycle of the signal, while in the positive half cycle of the signal, D1 is reverse biased and does not work, so the UA voltage value is not affected. Op amp U1A is a common rail-to-rail op amp like U1B. The voltage UA is connected to the in-phase terminal of pin 3 of U1A op amp after voltage division by R2 and R3. R2 mainly plays a role in protection and signal adjustment, and R3 also plays a role in signal adjustment and op amp offset adjustment. The op amp U1A is connected in follower working mode, which can directly transform the signal impedance, making it convenient for U1B to be used as the in-phase input signal. Therefore, for the voltage UA, the op amp U1B works in the in-phase amplification state. By adjusting the resistance value of each resistor, the positive and negative half-cycle gains of the signal can be easily adjusted to be the same, realizing the error-free and high-precision absolute value measurement of the signal under single power supply conditions. Resistor R4 mainly plays the role of isolation and offset adjustment. Because of the use of ordinary rail-to-rail op amps, the A / D converter range can be maximized, thereby improving the accuracy of signal measurement and reducing product costs.

[0044] In another embodiment, referring to Figure 5 As shown, a single-power rail-to-rail absolute value circuit does not have a signal follower circuit 5, the first end of the fourth resistor R3 is connected to the non-inverting input terminal of the first operational amplifier U1B, and the second end of the third resistor R2 is connected to the non-inverting input terminal of the first operational amplifier U1B.

[0045] Reference Figure 5 As shown, the absolute value operation processing circuit 3 further includes a second capacitor C2, one end of the second capacitor C2 is connected to the positive electrode of the first operational amplifier U1B, and the other end of the second capacitor C2 is grounded.

[0046] This improved design uses only one common rail-to-rail operational amplifier, and the waveform operations of the positive and negative half cycles are completed by the same operational amplifier. In extreme cases, the protection resistor R2 can also be removed to further simplify the design, save space and reduce costs.

[0047] The working principle and working process of this embodiment can refer to the corresponding contents of the above-mentioned embodiments.

[0048] The same or similar parts between the above-mentioned embodiments in this specification can be referenced to each other, and each implementation method focuses on the differences from other implementation methods, but it is not limited to the differences that cannot be replaced or superimposed on each other.

[0049] The above embodiments are only used to explain the technical solutions of the present invention rather than to limit them. Those skilled in the art should understand that any modification and equivalent substitution that does not depart from the spirit and scope of the present invention should fall within the protection scope of the claims of the present invention.

Claims

1. A single power rail-to-rail absolute value circuit, characterized in that: include: A positive half-cycle signal processing circuit, the positive half-cycle signal processing circuit comprising a first resistor and a positive signal elimination device, wherein a first end of the first resistor is connected to an input signal end, a first end of the positive signal elimination device is connected to a second end of the first resistor, and a second end of the positive signal elimination device is grounded; A negative half-cycle signal processing circuit, the negative half-cycle signal processing circuit comprising a second resistor and a negative signal elimination device, the first end of the second resistor is connected to the input signal end, the first end of the negative signal elimination device is connected to the second end of the second resistor, and the second end of the negative signal elimination device is grounded; An absolute value operation processing circuit, the absolute value operation processing circuit comprising a first operational amplifier, a non-inverting input terminal of the first operational amplifier is connected to the output terminal of the negative half-cycle signal processing circuit, and an inverting input terminal of the first operational amplifier is connected to the output terminal of the positive half-cycle signal processing circuit; The positive signal elimination device and the negative signal elimination device are both diodes; the positive electrode of the positive signal elimination device is connected to the second end of the first resistor, and the negative electrode of the positive signal elimination device is grounded; the positive electrode of the negative signal elimination device is grounded, and the negative electrode of the negative signal elimination device is connected to the second end of the second resistor; The positive signal elimination device and the negative signal elimination device are both Schottky diodes; Also included is a signal adjustment circuit, the signal adjustment circuit comprising: a third resistor, wherein a first end of the third resistor is connected to a second end of the second resistor, a first end of the third resistor is connected to a negative electrode of the negative signal elimination device, and a second end of the third resistor is connected to a non-inverting input end of the first operational amplifier; a fourth resistor, wherein a first end of the fourth resistor is connected to the second end of the third resistor, a first end of the fourth resistor is connected to the non-inverting input end of the first operational amplifier, and a second end of the fourth resistor is grounded; The absolute value operation processing circuit also includes: a fifth resistor, wherein a first end of the fifth resistor is connected to a second end of the first resistor, a first end of the fifth resistor is connected to a positive electrode of the positive signal elimination device, and a second end of the fifth resistor is connected to an inverting input end of the first operational amplifier; a sixth resistor, wherein a first end of the sixth resistor is connected to the second end of the fifth resistor, a first end of the sixth resistor is connected to the inverting input end of the first operational amplifier, and a second end of the sixth resistor is connected to the output end of the first operational amplifier; The model of the first operational amplifier is SGM8054.

2. A single power rail-to-rail absolute value circuit according to claim 1, characterized in that: It also includes a signal follower circuit, which includes a second operational amplifier, the second end of the third resistor is connected to the non-inverting input of the second operational amplifier, the first end of the fourth resistor is connected to the non-inverting input of the second operational amplifier, the inverting input of the second operational amplifier is connected to the output of the second operational amplifier, and the output of the second operational amplifier is connected to the non-inverting input of the first operational amplifier.

3. A single power rail-to-rail absolute value circuit according to claim 2, characterized in that: The signal follower circuit also includes: a seventh resistor, wherein a first end of the seventh resistor is connected to the output end of the second operational amplifier, and a second end of the seventh resistor is connected to the non-inverting input end of the first operational amplifier; A first capacitor, one end of the first capacitor is connected to the positive power supply electrode of the second operational amplifier, and the other end of the first capacitor is grounded.

4. A single power rail-to-rail absolute value circuit according to claim 2, characterized in that: The model of the second operational amplifier is SGM8054.

Images