JP2003273673A - Offset control device for variable gain amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an offset control device in which a time required for fixing the DC voltage level of an output voltage is shortened, circuit scale is reduced, the stability of a circuit is secured, and further, circuit configuration is simplified. <P>SOLUTION: A gain control circuit 1 outputs a control signal S for switching a gain. In response to the control signal S, an offset control circuit 3 outputs an offset control voltage Vref for keeping the voltage level of a reference DC voltage Vbase for the DC voltage level of an output voltage Vout. Besides, a variable gain amplifier 2 has a gain in response to the control signal S, inputs an input DC voltage Vin and the offset control voltage Vref from the offset control circuit and outputs the output voltage Vout kept at the voltage level of the reference DC voltage Vbase. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for offset control of a variable gain amplifier which makes it possible to keep an output DC voltage level constant. In particular, the present invention relates to a technique for offset control of a variable gain amplifier, which makes it possible to keep the output DC voltage level constant by generating an offset control voltage according to the gain, which offset occurs when the gain is switched. .

[0002]

2. Description of the Related Art FIG. 8 is a circuit diagram for explaining the outline of a conventional offset control device for a variable gain amplifier.

The offset control device shown in FIG. 8 includes a gain control circuit 81, a variable gain amplifier 82, and an offset control circuit 83. An AD converter 84 is connected downstream of the offset control device.

The operation of the offset control device configured as described above will be briefly described. As shown in FIG. 8, the offset control device shown in FIG. 8 controls the offset of the variable gain amplifier 82 by using the configuration of the feedback circuit. That is, in the offset control device shown in FIG. 8, the offset control circuit 83 operates so as to control the offset of the variable gain amplifier 82 based on the output voltage Vout from the variable gain amplifier 82. It enables the output voltage Vout to be constant. The output voltage Vout is AD-converted by the AD converter 84 in the subsequent stage and then input to the signal processing circuit.

Here, the offset of the variable gain amplifier 82 means that when a constant input voltage Vin is input,
That is, the DC voltage level of the output voltage Vout changes when the gain of the variable gain amplifier 82 is switched by the control signal S from the gain control circuit 81.

As described above, the conventional offset control device for the variable gain amplifier 82 controls the offset generated when the gain of the variable gain amplifier 82 is switched by using the configuration of the feedback circuit.

[0007]

However, the conventional offset control device is unstable because the circuit may oscillate by using the configuration of the feedback circuit. Further, since feedback is performed based on the output voltage Vout to control the offset, it takes time for the DC voltage level of the output voltage Vout to become constant.

Further, when the structure of the feedback circuit is designed by using the analog circuit, the circuit structure becomes complicated, so that it is difficult to design and analyze it, such as increase in simulation time. Further, in this case, the circuit scale becomes large, resulting in an increase in power consumption.

Therefore, in view of the above, an object of the present invention is to shorten the time required for the DC voltage level of the output voltage Vout to become constant, reduce the circuit scale, and ensure the stability of the circuit. An object is to provide an offset control device that can be realized with a simple circuit configuration.

[0010]

In order to solve the above-mentioned problems, the invention according to claim 1 provides a gain control circuit for outputting a control signal for switching a gain, and a control signal from the gain control circuit. In response, an offset control circuit that outputs a first offset control voltage for maintaining the DC voltage level of the output voltage at a reference voltage level, and a gain that responds to a control signal from the gain control circuit, Voltage and the first offset control voltage from the offset control circuit are input,
And a variable gain amplifier that outputs the output voltage.

According to the first aspect of the invention, the first offset control voltage that can be theoretically obtained in advance is input to the variable gain amplifier in response to the control signal for switching the gain from the gain control circuit. Therefore, the output DC voltage level can be made constant without using the configuration of the feedback circuit. Therefore, the stability of the entire circuit is increased, and when switching the gain, the time until the DC voltage level of the output voltage converges to the voltage level of the reference DC voltage can be shortened. Further, since it can be realized with a simple circuit configuration, it is possible to reduce the circuit scale, and accordingly it is possible to reduce power consumption. Further, compared to the case of designing a variable gain amplifier including an analog feedback circuit, it is possible to shorten the simulation time at the time of design and the number of steps.

The invention described in claim 2 is the same as claim 1.
In the variable gain amplifier offset control device described above, the offset control circuit responds to a control signal from the gain control circuit such that a DC voltage level of an output voltage is higher than the reference voltage level.
Second for giving the output voltage a predetermined offset
Of the offset control voltage, the variable gain amplifier inputs the input voltage and the second offset control voltage from the offset control circuit, outputs an output voltage having the predetermined offset, The offset control device of the gain amplifier binarizes the output voltage having the predetermined offset and then removes the predetermined offset by predetermined digital signal processing.

According to the invention of claim 2, the offset control circuit outputs a second offset control voltage for giving a predetermined offset to the output voltage,
After binarization, the signal processing circuit removes the predetermined offset. In this way, by performing the offset correction by using the arithmetic processing in the signal processing circuit as well, the offset is controlled with accuracy equal to or higher than that of the analog feedback circuit, even with respect to variations in semiconductor elements and variations due to temperature characteristics. it can.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. The same or corresponding portions are denoted by the same reference numerals in the referenced drawings, and detailed description thereof will not be repeated.

Generally, there are roughly two basic methods for offset control of a variable gain amplifier.

First, each method will be briefly described with reference to the drawings.

The first method is, as shown in FIG. 1, based on the output from the inverting amplifier 2, the input bias voltage to the inverting amplifier 2 (hereinafter referred to as "offset control voltage Vre").
The gain control circuit 1 is controlled by controlling
This is a method of controlling the offset of the inverting amplifier 2 that occurs when the gain is switched by the control signal S from.

The second method, as shown in FIG. 2, is to control the voltage level of the input signal based on the output from the inverting amplifier 2 so that the control signal S from the gain control circuit 1 is obtained. Inversion amplifier 2 that occurs when the gain is switched by
Is a method of controlling the offset of. It should be noted that the point common to both is that offset control is performed using the configuration of the feedback circuit, as in the conventional example.

Here, a specific description will be given with reference to FIG. 1 as an example.

The offset control device for a variable gain amplifier shown in FIG. 1 includes a gain control circuit 1 and an inverting amplifier 2.
And an offset control circuit 3. Further, as shown in FIG. 1, an input resistor R1 is connected between the input signal line and the inverting input terminal 2a of the inverting amplifier 2, and between the output signal line and the inverting input terminal 2a of the inverting amplifier 2. A feedback resistor R2 is connected to.

In general, the gain of the inverting amplifier 2 using an operational amplifier is determined by the ratio of the input resistance R1 and the feedback resistance R2. Thus, reversing the case of using the gain of the n steps as the gain of the amplifier 2, as shown in FIG. 1, the feedback resistor R1 is n analog switches sw ₁ to switch between these resistors and n resistors r ₁ ~r _n ~ Sw _n are connected. Then, the control signal S from the gain control circuit 1
A gain of n steps is realized by switching the _n analog switches sw _{1 to} sw _n . (In the following, n number of resistors r ₁ ~r _n and the analog switch sw ₁
Refer to FIG. 3 for a simplified description of ˜sw _n . The offset control circuit 3 inputs the offset control voltage Vref for controlling the offset to the non-inverting input terminal 2b of the inverting amplifier 2. Also,
The offset control circuit 3 is connected between the output signal line of the inverting amplifier 2 and the non-inverting input terminal 2b and forms a feedback loop. The offset here is the D of the output voltage Vout generated when the gain is switched.
It is the difference voltage between the C voltage level and the reference DC voltage Vbase. The output signal line of the inverting amplifier 2 is electrically connected to another semiconductor integrated circuit in the subsequent stage.

In order to obtain an output voltage Vout having a constant DC voltage level with respect to an analog input signal having a constant DC voltage level of the input voltage Vin, as shown in FIG. It can be realized by changing the characteristics.

FIG. 4 is a diagram showing the input / output characteristics of the variable gain amplifier shown in FIG. That is, although FIG. 4 shows the input / output characteristics a1 to a3 according to the gain of three stages, the offset control voltage Vref applied to the non-inverting input terminal 2b is Vref1, Vref2, Vr according to the gain of three stages.
By controlling with ef3, as shown in the figure, when the DC voltage level of the input voltage Vin of the analog input signal is constant at the level shown at the point a, even if the gain changes, the DC voltage level of the output voltage Vout becomes the point b. It can be kept constant at the level shown in.

The control of the offset control voltage Vref will be described here.

Generally, the output voltage Vout of the analog output signal according to the switching of the gain is

[0026]

[Equation 1] The offset control circuit 3 compares the DC voltage level of the output voltage Vout from the inverting amplifier 2 with the reference DC voltage Vbase, and outputs the output voltage Vou.
The offset control voltage Vref input to the non-inverting input terminal 2b of the inverting amplifier 2 is determined so that the DC voltage level of t matches the voltage level of the reference DC voltage Vbase.

As described above, the advantage of performing the offset control using the configuration of the feedback circuit is that the output voltage is
By designing so that Vout can accurately follow the voltage level of the target reference DC voltage Vbase,
That is, it is possible to perform control while absorbing individual variations of the semiconductor element. However, as described above, when performing the offset control using the configuration of the feedback circuit, the output voltage Vo generated when the gain is switched
The DC voltage level of the output voltage Vout becomes unstable during the period from when the DC voltage level of ut changes to when it returns to constant.

The offset control device shown in FIG. 2 also has the input / output characteristic diagram of FIG. 5 based on the comparison between the DC voltage level of the output voltage Vout and the voltage level of the reference DC voltage Vbase. As shown, offset control is performed by controlling the DC voltage level of the input voltage Vin input to the operational amplifier within the range indicated by the arrow in the figure according to the gain.

Based on the basic offset control method described above, the offset control device according to the present invention will be described below.

FIG. 6 is a diagram showing a configuration of an offset control device for explaining an embodiment of the present invention.

The offset control device shown in FIG. 6 is of a type that uses the method of controlling the offset control voltage Vref to perform the offset control in order to keep the DC voltage level of the output voltage Vout constant. And this offset control device
The gain control circuit 1, the inverting amplifier 2, and the offset control circuit 3 are provided. An AD converter 4 and a signal processing circuit 5 are connected to the subsequent stage of the inverting amplifier 2 as shown in FIG.

An input resistor R1 is connected between the inverting input terminal 2a of the inverting amplifier 2 and the input signal line.
Further, a feedback resistor R2 is connected to the feedback loop of the inverting amplifier 2. Note that these resistance values are variable, and the control signal S from the gain control circuit 1 switches the resistance values as appropriate to enable variable gain. Also,
The analog signal output from the inverting amplifier 2 is
After AD conversion by the D converter 4, the signal processing circuit 5
Sent to. The variable gain amplifier shown in the claims (see FIG.
(Corresponding to the variable gain amplifier shown in 1) includes the inverting amplifier 2, the input resistor R1, and the feedback resistor R2.

The offset control circuit 3 is connected between the gain control circuit 1 and the non-inverting input terminal 2b of the inverting amplifier 2. When the control signal S for switching the gain is input, the offset control circuit inputs the offset control voltage Vref (corresponding to the first offset control voltage) for controlling the offset to the non-inverting input terminal 2b of the inverting amplifier 2. To do.

As described above, the offset control device shown in FIG. 6 does not feed back the output voltage Vout from the inverting amplifier 2 to perform offset control, but inputs the control signal S from the gain control circuit 1. Then
This is mainly different from the offset control device shown in FIG. 3 in that the offset control is performed at the same time when the gain is switched.

Here, also in the offset control device shown in FIG. 6, between the input voltage Vin, the output voltage Vout, the offset control voltage Vref, the input resistance R1 and the feedback resistance R2, the same relational expression as in the above mathematical expression 1 is used. Is established.

If this equation 1 is used, DC of the input voltage Vin
When the voltage level is constant and the gain changes, the output voltage Vo
The offset control voltage Vref required to keep the DC voltage level of ut constant can be theoretically obtained in advance. That is, the offset control voltage Vref corresponding to the gain can be theoretically calculated by the equation 1 without feeding back the output voltage Vout to determine the offset control voltage Vref. Therefore, the offset control circuit 3 receives the control signal S for switching the gain from the gain control circuit 1 and outputs the offset control voltage Vref according to the switching of the gain as described with reference to FIG. Thus, the DC voltage level of the output voltage Vout can be set to the voltage level of the reference DC voltage Vbase without being affected by the gain switching.

As described above, the offset control device according to this embodiment inverts the theoretically decidable offset control voltage Vref in response to the control signal S for switching the gain without using the configuration of the feedback circuit. Input to the non-inverting input terminal 2b of the amplifier 2. Therefore, the DC voltage level of the output voltage Vout can be made constant without using the configuration of the feedback circuit. Therefore, the stability of the entire circuit is increased, and when switching the gain, it is possible to shorten the time until the DC voltage level of the output voltage Vout converges to the voltage level of the reference DC voltage Vbase. Further, since it can be realized with a simple circuit configuration, it is possible to reduce the circuit scale, and accordingly it is possible to reduce power consumption.
Further, compared to the case of designing a variable gain amplifier including an analog feedback circuit, it is possible to shorten the simulation time at the time of design and the number of steps.

<Modification> As described above, the offset control device shown in FIG. 6 controls the offset by inputting the offset control voltage Vref obtained based on Equation 1 to the non-inverting input terminal 2b of the inverting amplifier 2. To do.
However, Equation 1 is a formula that is satisfied under ideal conditions, and does not take into consideration variations in semiconductor elements that form a circuit and minute variations in characteristics due to the influence of temperature characteristics and the like.

In the case of the offset control device shown in FIG. 3, since the offset control is performed by the feedback control as described above, it is possible to always change the optimum value to follow variations. On the other hand, in the case of the offset control device shown in FIG. 6, as described above, the offset control voltage Vref obtained from Equation 1 is used to perform the offset control by the feedforward control, so that the influence of variations is absorbed. It is difficult to control.

FIG. 7 is a diagram for explaining a modified example of this embodiment. FIG. 7 is a diagram showing the DC voltage level of the output voltage Vout ′ in the case where variations in semiconductor elements and variations in characteristics due to influences of temperature characteristics and the like are taken into consideration.

That is, in this modification, as shown in FIG. 7, the DC voltage level of the output voltage Vout is the reference DC voltage V.
Output voltage Vout 'which is higher than the voltage level of base by ΔVout
It is a conceptual diagram which shows the voltage level of. Then, the offset control device according to the present modified example uses the reference DC voltage Vb
Output DC voltage Vo higher than ase voltage level by ΔVout
Control so that ut 'can be output.

[0042]

[Equation 2] The above formula 2 is a modification obtained by adding ΔVout to the output DC voltage Vout of the above formula 1. Thus, when the offset control voltage Vref (corresponding to the second offset control voltage) obtained from Equation 2 is input to the inverting amplifier 2, the output voltage Vout ′ shown in FIG. 7 can be obtained.
Then, the output voltage Vout ′ is AD-converted by the AD converter 4, and then the signal processing circuit 5 performs arithmetic processing.

Here, the signal processing circuit 5 outputs the output voltage Vou
An arithmetic process for removing an offset (corresponding to a predetermined offset) which is a difference between the DC voltage level of t ′ and the voltage level of the reference DC voltage Vbase is performed. Therefore, it becomes possible to perform the offset control in consideration of the variation of the offset due to the variation of various characteristics.

As described above, the offset control device according to the present modification controls the offset so that the DC voltage level of the output voltage Vout 'may be slightly offset, and further, the offset is controlled in the signal processing circuit 5 after binarization. Since the above is eliminated, it is possible to absorb the variation in the characteristics of the semiconductor circuit element and the error due to the temperature characteristics. Further, the higher the conversion accuracy of the AD converter 4 for binarization used in the subsequent stage of the offset control device, the higher the accuracy of offset correction in the signal processing circuit 5.

In the above embodiment, the inverting amplifier 2
However, the present invention is not limited to this embodiment, and other variable gain amplifiers can theoretically show the relationship between the input voltage, the output voltage, the gain, and the offset control voltage. The present invention can be implemented in the same manner as long as the circuit can be obtained as follows.

[0046]

As described above, according to the present invention, the offset control voltage that can be theoretically determined is input to the variable gain amplifier in response to the control signal for switching the gain without using the configuration of the feedback circuit. Therefore, the output voltage level can be made constant without using the configuration of the feedback circuit. Therefore, the stability of the entire circuit is increased, and when switching the gain, the time until the DC voltage level of the output voltage converges to the voltage level of the reference DC voltage can be shortened. Further, since it can be realized with a simple circuit configuration, it is possible to reduce the circuit scale, and accordingly it is possible to reduce power consumption. Further, compared to the case of designing a variable gain amplifier including an analog feedback circuit, it is possible to shorten the simulation time at the time of design and the number of steps.

[Brief description of drawings]

FIG. 1 is a basic circuit diagram of an offset control device of a variable gain amplifier that controls an offset control voltage to perform offset control.

FIG. 2 is a basic circuit diagram of an offset control device of a variable gain amplifier that controls an input DC voltage level to perform offset control.

FIG. 3 is a diagram showing the offset control device shown in FIG. 1 in which a resistance portion is simplified.

FIG. 4 is a diagram for explaining input / output characteristics of the offset control device shown in FIG. 3 and FIG. 6 described later.

5 is a diagram for explaining input / output characteristics of the offset control device shown in FIG.

FIG. 6 is a circuit diagram of an offset control device for a variable gain amplifier according to an exemplary embodiment of the present invention.

FIG. 7 is a conceptual diagram of a DC voltage level of an output voltage for explaining a modified example of the embodiment.

FIG. 8 is a schematic diagram for explaining a conventional offset control device for a variable gain amplifier.

[Explanation of symbols]

1 Gain control circuit 2 inverting amplifier 2a Inversion input terminal 2b Non-inverting input terminal 3 Offset control circuit 4 AD converter 5 Signal processing circuit Vin input voltage Vout, Vout 'Output voltage Vref Offset control voltage R1 input resistance (group) R2 feedback resistance (group) S control signal

Claims (2)

[Claims] 1. A gain control circuit for outputting a control signal for switching a gain, and a first control circuit for maintaining a DC voltage level of an output voltage at a reference DC voltage level in response to a control signal from the gain control circuit. An offset control circuit that outputs an offset control voltage of 1, and a gain that responds to a control signal from the gain control circuit, and that inputs an input voltage and the first offset control voltage from the offset control circuit, An offset control device for a variable gain amplifier, comprising: a variable gain amplifier that outputs the output voltage. 2. The offset control device for a variable gain amplifier according to claim 1, wherein the offset control circuit responds to a control signal from the gain control circuit, and a DC voltage level of an output voltage is the reference DC voltage. Outputting a second offset control voltage for giving the output voltage a predetermined offset so as to exceed the level, and the variable gain amplifier outputs the input voltage and the second offset from the offset control circuit. A control voltage is input, and an output voltage having the predetermined offset is output, and the offset control device of the variable gain amplifier binarizes the output voltage having the predetermined offset,
An offset control apparatus for a variable gain amplifier, wherein the predetermined offset is removed by predetermined digital signal processing.