JPS63132510A - Programmable gain-controlled amplifier - Google Patents

Abstract

PURPOSE:To eliminate the need to arrange many high-accuracy resistors and to reduce the cost of a programmable gain-controlled amplifier by controlling the gain of the amplifier according to a duty ratio which is set variably by a pulse width/voltage converting circuit. CONSTITUTION:The pulse width/voltage converting circuit 6 is provided with two analog switches S1 and S2, a filter for smoothing consisting of a resistance R2 and a capacitor C2, and a duty ratio varying circuit 7 as a means for varying and setting the duty ratio T1/T2 of a pulse (e) to a necessary value. The duty ratio varying circuit 7 is connected directly to the analog switch S1 and also connected to the other analog switch S2 through an inverter 8. The output E0 of the programmable gain-controlled amplifier is controlled by the pulse width/voltage converting circuit 6 to a value corresponding to the duty ratio T1/T2 to perform control to desired gain.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a programmable gain control amplifier used, for example, in a data acquisition system.

(Prior Art) Amplifiers used in data acquisition systems and the like are required to be capable of programmable gain control.

An example of such a conventional programmable gain control amplifier is the one shown in FIG.

The programmable gain control amplifier includes a non-inverting amplifier 10 and a plurality of resistors Rn to R connected in a ladder configuration.
n and analog switches So to Sn. The analog switches S+t to Sn are turned on and off by gain control signals Go to Gn, respectively.

Depending on which of the analog switches So to 3n is turned on by the gain control signals Gll to Qn, the ratio of the external resistances of the non-inverting amplifier 10 is switched, and the gain is controlled.

For example, assuming that the analog switch S11 is turned on by the gain control signal Gu and the other analog switches S+2 to Sn are all turned off, the gain A2 is set as shown in the following equation.

A2=Eo/Ei =1+ (Ru/ (R+z+R+3+-Rn))...
-(1) Here, Ei is the input voltage and EO is the output voltage.

(Problem to be Solved by the Invention) However, in the programmable gain control amplifier described above, as shown in equation (1) above, the gain A2 is determined by the resistance values of the plurality of resistors Ru to Rn. , in order to program the gain A2 with high accuracy and fine detail, a large number of high-precision resistors and a large number of analog switches are required, which increases the cost and also makes it difficult to use even if a large number of resistors are used. However, there is a problem in that it is difficult to precisely control the gain A2.

The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to provide a programmable gain control amplifier that is capable of highly accurate and fine gain control and that can reduce costs.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention provides a comparator in which an input voltage is input to one input terminal, and an integral unit that integrates the output of the comparator. and a means for variably setting the duty ratio of the pulse to a required value, converts the input output of the integrator into a voltage according to the duty ratio, and applies this converted voltage to the other of the comparators. The present invention further comprises a pulse width/voltage conversion circuit that is input to an input terminal and controls the output of the integrator using the duty ratio.

(Operation) The output of the integrator is input to the pulse width/voltage conversion circuit and converted into a voltage according to the set duty ratio. This converted voltage is fed back to the comparator.

A comparator compares the converted voltage with the input voltage, and controls the output of the integrator so that the converted voltage and the input voltage are equal.

The output of the integrator is controlled by the duty ratio set by the pulse width/voltage conversion circuit.

That is, gain control is performed by variable setting of the duty ratio.

(Example) Hereinafter, an example of the present invention will be described based on FIGS. 1 to 3.

The first factor is a circuit diagram showing the overall configuration, FIG. 2 is a circuit diagram of the pulse width/voltage conversion circuit, and FIG. 3 is a waveform diagram of pulses output from the variable duty ratio circuit.

First, to explain the configuration, in FIG. 1, 1 is a comparator,
An inverting input terminal (-) of the comparator 1 is connected to an input terminal 2 of the input voltage Ei. An integrator 3 for integrating the output of the comparator 1 is connected to the next stage of the comparator 1.

The integrator 3 is composed of an operational amplifier 4, a resistor R+, and a capacitor C1, and has an output voltage Eo at its output terminal.
The output terminal 5 of is connected.

A feedback line is connected between the output terminal 5 and the non-inverting input terminal (+) of the comparator 1, and a pulse width/voltage conversion circuit 6 is connected to this feedback line.

The pulse width/voltage conversion circuit 6 includes two analog switches S+ and 82, a smoothing filter consisting of a resistor R2 and a capacitor C2, and a duty ratio (T) of the pulse e.
A variable duty ratio circuit 7 is provided as means for variably setting the I/T2) to a required value. The variable duty ratio circuit is composed of a microprocessor or the like.

The variable duty ratio circuit 7 is directly connected to the analog switch S+, and is also connected via the inverter 8 to another analog switch S2. The two analog switches S+ and S2 are alternately controlled on and off by variable duty ratio pulses e as shown in FIG. 3 outputted from the variable duty ratio circuit 7.

Next, the action will be explained.

Using FIG. 2, the operation of the pulse width/voltage conversion circuit 6 will be explained first. Pulse width/voltage conversion circuit 6 shown in Fig. 2
Let the input voltage be El and the output voltage be E2.

The two analog switches S+ and S2 are activated by a pulse e whose duty ratio (TI/T2) is variable as shown in FIG.
is alternately turned on and off, the input voltage E1 is switched by the alternate on and off of this analog switch S+, 82, and its switching output is applied to the resistor R2.
and a filter consisting of capacitor C2.

As a result, the output voltage E2 expressed by the following equation is obtained from the pulse width/voltage conversion circuit 6.

E2 = E+ ・(TI/T2) ・・
・(2) In the circuit of FIG. 1, the input voltage E1 and the output voltage E2 in the above equation (2) are the input voltages to the output of the integrator 3 and the non-inverting input terminal (+) of the comparator 1, respectively. Become. Therefore, the pulse width/voltage conversion circuit 6 changes the output of the integrator 3 to the set duty ratio (T
This converted voltage E2 is input to the non-inverting input terminal (+) of the comparator 1.

Next, the operation of the circuit shown in FIG. 1 will be explained. Initially, integrator 3
The output voltage Eo is zero, and the duty ratio of the pulse e in the pulse width/voltage conversion circuit 6 is (TI/T2).
It is assumed that this is set to .

When the (+) input voltage Ei is input to the input terminal 2, the comparator 1 outputs a (+) saturation voltage at a predetermined level. The integrator 3 integrates this (-) saturation voltage, and its output increases in the (+) direction.

This (+) output voltage of the integrator 3 is converted by the pulse width/voltage conversion circuit 6 into a voltage E2 according to the duty ratio (TI/T2) as shown in the above equation (2), and this conversion Voltage E2 is input to the non-inverting input terminal (+) of comparator 1.

Then, the comparator 1 compares the feedback converted voltage E2 and the input voltage Ei, and the converted voltage E2>
When the relationship of the input voltage Ei is reached, the output of the comparator 1 is inverted to a (+) saturation voltage of a predetermined level.

Due to this inversion of the output of comparator 1, integrator 3 starts integrating in the opposite direction, and its output starts to decrease.

Due to the decrease in the output of the integrator 3, the double input voltage of the comparator becomes larger than the input voltage Ei>change Ig! When the voltage E2 is reached, the output of the comparator 1 is again inverted to the (-) saturation voltage.

The above operation is repeated, converting voltage E2 and input voltage Ei
The output of the integrator 3 is controlled so that .

Therefore, the output of the integrator 3, in other words, the output E of the programmable gain control amplifier.

is controlled to a value corresponding to the duty ratio <TI/T2) set by the pulse width/voltage conversion circuit 6. Then, the gain is controlled to a desired value by appropriately variably setting the duty ratio (TI/T2).

At this time, the set gain A1 is given by the following equation from equation (2) above.

AI −Eo /E i =T2 /T+
-(3) That is, the set gain A1 is defined by the reciprocal of the duty ratio.

Since the duty ratio can be digitally controlled relatively easily and with high precision using the variable duty ratio circuit 7, it is necessary to use a high-precision and expensive resistor as in the conventional example shown in FIG. Programmable gain control with extremely high stability is possible without the need for multiple devices.

The programmable gain control amplifier according to this embodiment has extremely suitable characteristics for application to a data acquisition system configured by adding a multiplexer, an AID converter, etc. to the programmable gain control amplifier.

[Effect of the Invention 1] As explained above, according to the configuration of the present invention, gain control is performed by the duty ratio that is variably set in the pulse width/voltage conversion circuit, so highly accurate and fine gain control is possible. Furthermore, since it is not necessary to provide a large number of high-precision resistors, there is an advantage that costs are reduced.

[Brief explanation of the drawing]

1 to 3 show an embodiment of the programmable gain control amplifier according to the present invention. FIG. 1 is a circuit diagram showing the overall configuration, and FIG. 2 is a circuit diagram showing an extracted pulse width/voltage conversion circuit. 3 are waveform diagrams of pulses output from the variable duty ratio circuit, and FIG. 4 is a circuit diagram showing a conventional programmable gain control amplifier. 1: Comparator, 2: Input terminal, 3: Integrator, 5: Output terminal, 6: Pulse width/voltage conversion circuit, 7: Duty ratio variable circuit. Figure 1 Figure 2

Claims (1)

[Claims] a comparator into which an input voltage is input to one input terminal; an integrator that integrates the output of the comparator; and means for variably setting the duty ratio of the pulse to a required value; is converted into a voltage according to the duty ratio,
A programmable gain control amplifier comprising: a pulse width/voltage conversion circuit that inputs the converted voltage to the other input terminal of the comparator and controls the output of the integrator according to the duty ratio.