KR20020012862A - Non-inverting gain control Amplifier having functions of DC level shift and low-pass-filter - Google Patents

Abstract

PURPOSE: A non-inversion gain control amplifier having a DC voltage level shift function and a low frequency filtering function is provided, which reduces a layout area and power consumption and improves an offset voltage characteristics. CONSTITUTION: The non-inversion gain control amplifier comprises an operational amplifier, a feedback capacitor(C21) and a feedback variable resistor(R25) having a low frequency filtering function, and input resistors(R21,R23) and variable resistors(R22,R24) for a voltage gain and DC voltage level shift function. The feedback capacitor and the feedback variable resistor determine a frequency characteristics of a low frequency filter, and its amplitude is R25/R21 and its phase is inverted. The resistor(R21,R23) and the variable resistors(R22,R24,R25) determine a DC voltage gain value. The variable resistor(R24) and the variable resistor(R25) are connected with an external input signal(Vofst) to perform the DC voltage level shift function.

Description

Non-inverting gain control amplifier having functions of DC level shift and low-pass-filter}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to semiconductor integrated circuits, and more particularly, to a non-inverting gain control amplifier that performs a low frequency filtering function, a DC voltage level shifting function, and a voltage gain adjusting function employed in digital video disc players and compact disc read / write.

Non-inverting gain-controlled amplifiers are used at the input stage of the system where they need to be processed into signals suitable for processing the input signal. When a non-inverting gain control amplifier is used in a video disc player and a compact disc, the output level of the signals picked up by the photodiode is different and there is noise. Shift the level to a level that is easy to handle.

1 is a circuit diagram showing an example of a conventional non-inverting gain control amplifier.

Conventional non-inverting gain control amplifier shown in Figure 1 consists of three stages,

The first stage includes an operational amplifier 10, a resistor R11 between the input signal Vin and the negative input terminal of the operational amplifier 10, a negative feedback capacitor C11, and a negative feedback resistor R12.

The second stage is the operational amplifier 12, the resistor R13 between the output 100 of the first stage and the positive input terminal of the operational amplifier 12, the external input terminal Vc and the operational amplifier 12 for voltage gain control. Variable resistor (R15) between positive input terminal, voltage gain control external input terminal (Vc) and resistor (R14) between negative input terminal of operational amplifier 12, output terminal 110 of operational amplifier 12 and A variable resistor (R16) is provided between the negative input terminals of the operational amplifier 12.

The third stage is the operational amplifier 14, the resistance (R17) between the output 110 of the second stage and the negative input terminal of the operational amplifier 14, the external input terminal (Vofst) and the operational amplifier (for DC voltage level shift) 14 is provided with a resistor R18 between the negative input terminal and the output terminal Vo and a resistor R19 between the negative input terminal of the operational amplifier 14.

In the three stages described above, the first stage performs the low frequency filtering function, the second stage adjusts the voltage gain, and the last stage performs the DC voltage level shift function, respectively.

The conventional circuit that performs the three functions in the above steps should be designed in consideration of the electrical characteristics of the operational amplifier used, in particular the offset voltage. This is because the input offset voltage inherently possessed by the operational amplifier may appear as a large output offset voltage by the device constant value constituting the circuit around the operational amplifier.

For example, when the input offset voltage of the first operational amplifier 10 is Voff, even when the input signal Vin is the same as the external application signal VR for setting the operation reference voltage, the output offset voltage having the same value as in Equation 1 is obtained. It appears at the output 100 of the first stage.

If the operational amplifier 12 of the second stage also has an input offset voltage of Voff, the output offset voltage of the value shown in Equation 2 appears in the output 110 of the second stage even when the input signal of the second stage is zero. .

Similarly, current I17 flows through R17 due to Voff of the operational amplifier 14 of the third stage. Since the output is determined by the current I17 flowing in the resistor R17 and the current I18 flowing in the resistor R18, the desired output voltage is not obtained.

As described above, in the conventional non-inverting gain control amplifier described above, three stages of circuits are required, and since operational amplifiers are used in each stage, the layout area is considerably large, and power consumption is increased. In particular, since the unique offset voltage generated at each stage continues to be transferred to the next stage and accumulates, there is a disadvantage of degrading the electrical characteristics of the circuit.

Accordingly, an object of the present invention is to provide a non-inverting gain control amplifier which performs a low frequency filtering function, a voltage gain control function and a DC voltage level shift function while reducing layout area and power consumption and improving output offset voltage characteristics. .

In order to more fully understand the drawings used in the detailed description of the invention, a brief description of each drawing is provided.

1 is a circuit diagram showing an example of a conventional non-inverting gain control amplifier.

2 is a circuit diagram illustrating a non-inverting gain control amplifier according to a first embodiment of the present invention.

3 is a circuit diagram illustrating a non-inverting gain control amplifier according to a second embodiment of the present invention.

4 is a computer simulation waveform diagram of signals in the operation of the conventional circuit shown in FIG. 1 (when the input offset voltage is 20 [mV; mili-volts]).

FIG. 5 is a computer simulation waveform diagram of signals in the operation of the circuit according to the first embodiment shown in FIG. 2 (when the input offset voltage is 20 mV).

FIG. 6 is a computer simulation waveform diagram of signals in the operation of the conventional circuit shown in FIG. 1 (without input offset voltage). FIG.

FIG. 7 is a computer simulation waveform diagram of signals in the operation of the circuit according to the first embodiment shown in FIG. 2 (without an input offset voltage).

The non-inverting gain control amplifier of the present invention for achieving the technical problem is connected between the output terminal of the operational amplifier, the operational amplifier and the negative input terminal of the operational amplifier to determine the frequency characteristics of the low frequency filter, the output of the operational amplifier Variable resistor connected between terminal and negative input terminal of operational amplifier to adjust voltage gain, Variable resistor connected to external input terminal for DC voltage level shift and negative input terminal of operational amplifier to control voltage gain, operation A resistor is connected between the external input terminal for setting the reference voltage and the negative input terminal of the operational amplifier, and is connected between the external input terminal for setting the operation reference voltage and the positive input terminal of the operational amplifier to set the operation reference voltage and gain the voltage. Variable resistor to adjust the resistance between the external input terminal and the positive input terminal of the operational amplifier. It is characterized by including.

In addition, the non-inverting gain control amplifier according to the present invention may further include a capacitor between the positive input terminal of the operational amplifier and the power supply voltage.

As described above, the present invention reduces the number of operational amplifiers used in comparison with conventional circuits, thereby reducing layout area and power consumption. In particular, since the offset voltage characteristic is improved, there is an advantage that the low frequency filter function, the voltage gain control function, and the DC voltage level shift function, which have improved electrical characteristics, can be performed.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. For each figure, like reference numerals denote like elements.

2 is a circuit diagram of a non-inverting gain control amplifier according to a first embodiment of the present invention.

Referring to FIG. 2, the non-inverting gain control amplifier according to the first embodiment of the present invention includes an operational amplifier, a feedback capacitor having a low frequency filtering function, a feedback variable resistor, an input resistance and a variable for a voltage gain and a DC voltage level shift function. With resistance.

The feedback capacitor C21 and the feedback variable resistor R25 determine the frequency characteristics of the low frequency filter, the magnitude of which is R25 / R21, and the phase is inverted. The resistors R21 and R23 and the variable resistors R22, R24 and R25 determine a DC voltage gain value. The variable resistor R24 and the variable resistor R25 are coupled to an external input signal Vofst to perform a DC voltage level shift function.

First, we will see if the circuit performs low frequency filter function, voltage gain control function and DC voltage level shift function.

The cutoff frequency fc of the non-inverting gain control amplifier shown in FIG. 2 has a value as shown in Equation 3 below.

In addition, if the variable resistor R24 and the variable resistor R25 are the same, the DC voltage gain Av has the same value as in Equation 4.

When the circuit is manufactured in a semiconductor integrated circuit, the resistance values of R22 and R24 (also R25) can be arbitrarily selected by a designer using a resistor string, a switch connecting the resistors, and a digital control signal for turning the switch on and off. Therefore, the voltage gain value can be changed accordingly.

Also, DC voltage level shift function is performed by using R24 and external input signal terminal (Vofst). For example, when 2.5V (Volts) is applied to the external input terminal VR for operating reference voltage setting and 2.5V is also applied to the external input terminal Vin, the positive input terminal 200 of the operational amplifier 20 is 2.5V. Therefore, since the negative input terminal of the operational amplifier also becomes 2.5V, no current flows through the resistor R23. However, if the external input terminal signal Vofst is 3.35V, the offset current Iofst has the same value as in Equation 5 in the input variable resistor R24.

This offset current flows through the feedback variable resistor R25 of the operational amplifier. If the variable resistor R24 is equal to the variable resistor R25, the voltage drop Vdrop of R25 (that is, R24) due to this offset current has the same value as in Equation (6).

Therefore, the final voltage appearing at the output terminal Vo is expressed by Equation 7.

That is, it makes DC output voltage level shift function by making the desired output voltage of 1.65V and supplying it to the next stage.

3 is a circuit diagram of a non-inverting gain control amplifier according to a second embodiment of the present invention.

Referring to FIG. 3, the non-inverting gain control amplifier according to the second embodiment of the present invention includes an operational amplifier 30, a feedback capacitor C31 having a low frequency filtering function, a feedback variable resistor R35, and an input for voltage gain. Resistors R31 and R33, variable resistors R32 and R34, and capacitor C32 for improving the frequency response characteristics of the low frequency filter are provided.

Hereinafter, the operation of the non-inverting gain control amplifier circuit according to the second embodiment of the present invention will be described with reference to FIG. 3.

The components in FIG. 3 coincide with each other in FIG. 2 but differ only in the capacitor C32 added to FIG. This capacitor C32 only affects the order of the low frequency filter without affecting other functions, and this description will be mainly given here.

In order to calculate the cutoff frequency in FIG. 3, first, when the transfer function between the input signal terminal Vin and the positive input terminal 300 of the operational amplifier 30 is obtained, the resistances R32 and R31 are equal to Equation 8; Has a value.

When the parallel resistance is separately calculated in Equation 8, the same value as Equation 9 is obtained.

Based on Equation 9, Equation 8 is rearranged to obtain Equation 10.

Similarly, when the transfer function between the positive input terminal V300 and the output terminal Vo of the operational amplifier is obtained, it has the value shown in Equation (11).

The transfer function between Vin and Vo from Equations 10 and 11 is equal to Equation 12.

It was found that the second low frequency filter operates as above. For the design of low frequency filter with higher order than 2nd order, capacitors are connected in parallel in front of R32 next to external input signal terminal (VR) for operation reference voltage setting, so that one node is connected to node 300 and the other is grounded (GND). Just add a circuit.

As described above, since the non-inverting gain control amplifier according to the present invention is understood to be equivalent to the conventional non-inverting gain control amplifier shown in FIG. 1 in terms of function, the present invention looks at whether the offset voltage characteristic is improved.

Considering the circuit of FIG. 1, which is a conventional circuit, and FIG. 2, which is an embodiment of the present invention, based on the input offset voltage, it can be seen that the improvement is intuitively made by comparing the number of operational amplifiers constituting the circuit. Assume that the operational amplifier used in the conventional circuit is the same as the electrical characteristics of the operational amplifier used in the embodiment of the present invention, the voltage gain is 1.

In the conventional circuit shown in Fig. 1, the offset voltages of the first, second and third stages are added to each other and appear at the output terminal Vo. However, in the case of the present invention using one operational amplifier as can be seen in the embodiment of the present invention, an offset voltage of about one third is expected in comparison with the conventional circuit. Moreover, the omission of two op amps also reduces the area of the chip occupied by the circuit, giving the circuit designer space to better design offset characteristics as well as other electrical characteristics of the op amp. Therefore, considering only the offset voltage, it is possible to design a circuit with much improved performance than the conventional circuit.

FIG. 4 is a computer simulation of the electrical characteristics at the output terminal Vo when the offset voltage of 20 mV and 2.5 V DC are applied to the input terminal Vin in the conventional non-inverting gain control amplifier shown in FIG. The waveform diagram is shown.

5 is a computer simulation of the electrical characteristics at the output terminal Vo when an offset voltage of 20 mV and a 2.5 V DC voltage are applied to the input terminal Vin of the non-inverting gain control amplifier according to the present invention shown in FIG. 2. The waveform diagram is shown. In FIG. 4, the value of the output terminal Vo is 2.1962V. This error is about 0.5462V compared to the design target of 1.65V. On the other hand, in FIG. 5, the output terminal Vo has a value of 1.4284V, resulting in an error of 0.2216V.

FIG. 6 is a computer simulated waveform diagram assuming that an ideal operational amplifier without offset voltage is used in the conventional non-inverting gain control amplifier circuit shown in FIG.

FIG. 7 is a computer simulated waveform diagram assuming that an ideal operational amplifier without offset voltage is used in the non-inverting gain control amplifier circuit of FIG. 2 according to the present invention. In the absence of an offset voltage, each circuit has no significant difference in output characteristics. Thus, even in ideal cases, the small number of operational amplifiers can be advantageous in many ways.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described above, the non-inverting gain control amplifier circuit according to the present invention has the advantage of performing a low frequency filter function, a voltage gain control function and a DC voltage level shift function while reducing layout area and power consumption and improving offset voltage characteristics. have.

Claims (3)

Output node; An operational amplifier having a positive input terminal and a negative input terminal and having an output terminal connected to the output node; A first capacitor connected between the output node and the negative input terminal of the operational amplifier to determine a frequency characteristic of the low frequency filter; A first resistor connected between the output node and the negative input terminal of the operational amplifier to determine a frequency characteristic of the low frequency filter; A second resistor connected between the negative input terminal of the operational amplifier and an external input terminal for DC voltage level shift to perform a DC voltage level shift function together with the first resistor; A third resistor connected between the negative input terminal of the operational amplifier and an external input terminal for setting an operation reference voltage to perform an operation reference voltage setting and a DC voltage gain adjusting function; A fourth resistor connected between the positive input terminal of the operational amplifier and the external input terminal for setting the operation reference voltage to perform an operation reference voltage setting and a DC voltage gain adjusting function; And And a fifth resistor connected between the positive input terminal of the operational amplifier and an external input signal terminal to perform a DC voltage gain adjusting function. The method of claim 1, wherein the first resistor, the second resistor and the fourth resistor, A non-inverting voltage gain amplifier comprising a variable resistor. The method of claim 1, wherein the non-inverting voltage gain amplifier, And a second capacitor connected between the positive input terminal of the operational amplifier and a power supply voltage.