JPS63110805A - Programmable gain amplifier - Google Patents

Abstract

PURPOSE:To reduce the number of parts by operating a gate means with the aid of a pulse obtained by modulating pulse width outputted from a pulse width modulation means, permitting a filter circuit to amplify an input voltage fetched from the gate means and regarding it as an output voltage. CONSTITUTION:If a duty ratio setting means 10 is set so as to generate a reference voltage Vref, a comparator 22 in the pulse width modulation circuit 20 modulates a triangular wave W with a period T into a pulse P with a pulse width tON due to the level of the voltage Vref, changes over a switch 30 with the aid of the pulse P and drives an active filter circuit 40. It converts a pulse string composed of an input voltage Vi and a peak value Vi at a ground level into a current satisfying V01 =D.Vi according to the duty ratio D, simultaneously gives K-fold gains, and outputs an output voltage satisfying V0=K.D.Vi. Thus the gain can be made highly accurate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a programmable gain amplifier whose gain (amplification degree) 'f: can be changed depending on the level of input voltage.

[Conventional technology]

- In the 1+ circuit, there is a demand for an amplifier that can change the gain of the amplifier circuit depending on the level of the input voltage.

However, in such an amplifier, the gain must be accurately known.

FIG. 4 is a block diagram showing an example of the above-mentioned conventional amplifier, where 1 is an operational amplifier, Ri, Rfn and Rs are resistors, and 81 to Sn are switches. and,
vl represents the input voltage, and vO represents the output voltage.

Next, the operation will be explained.

In the conventional amplifier configured as shown in FIG. 4, Rfi Vo=(1+(/R,) )Vi,,,,,,
, (1) However, Rfi: Rf□, Rf21...-, R
With fn, it is possible to obtain an output voltage Vo whose gain is changed according to the level of the input voltage Vt.

[Problem that the invention seeks to solve]

Conventional amplifiers are configured as described above, so if the gain is divided into sections such that, for example, at least one switch S1 and resistor R1 are required for one gain, the number of components will increase. , it becomes practically impossible to fine-grain the gain.

In addition, switches S such as relay contacts and analog fist switches are also available.
When using S~Sn, the switches S~Sn have non-constant on-resistances r1~rn.9th, each on-resistance r1~r
Since n affects the gain, the gain cannot be easily determined using the Tl+ formula, and Vo=(1+ ((Rf
1 +r 1 yRs ]) V i .=(2) However, rl:rl+r'2+"..."*rn. As a result, there are problems such as variations in the set gains depending on the on-resistances r to rn.

This invention was made in order to solve the above-mentioned problems, and its purpose is to obtain a programmable gain amplifier that can be constructed with a small number of parts and that allows for high precision gain and fine segmentation. do.

[Means for solving problems]

The programmable gain amplifier according to the present invention modulates the pulse width with the output of the duty ratio setting means, and adjusts the input voltage to a predetermined gain via the gate means according to the duty ratio of the pulse output from the pulse width modulation means. The configuration is such that it can be incorporated into a filter circuit having a

[Effect]

The programmable gain amplifier in this invention is
The gate means is operated by a pulse whose pulse width is modulated, which is output from the pulse width modulation means, and the input voltage taken in through the gate means is amplified by the filter circuit to produce an output voltage.

〔Example〕

FIG. 1 is a block diagram showing a programmable gain amplifier according to an embodiment of the present invention, and the same parts as in FIG. 4 are given the same reference numerals.

In FIG. 1, 10 indicates a duty ratio setting means,
For example, it is constituted by a DC voltage generation circuit that generates a reference voltage Vreft-. Reference numeral 20 denotes a pulse width modulation circuit as a pulse width modulation means, which is composed of a triangular wave generation circuit 21, a duty ratio setting means 10, and a comparator 22 which receives the output of the triangular wave generation circuit 21 as input. 30 indicates a switch as gate means, and the pulse width modulation circuit 20
The contact piece 30r is connected to the contact point 30a by the pulse output from the
Alternatively, it can be switched to the 30b side. 40 is
For example, an active filter circuit as a filter circuit with a gain of KtW is shown, and an operational amplifier 1. Resistance R1, Rf, Rs
, =f, and consists of capacitors C and C2. R engineering, R2
and R9 indicates resistance.

Next, the operation will be explained.

The programmable gain amplifier of the present invention configured as shown in FIG. The voltage Vref is applied to the comparator 22 of the pulse width modulation circuit 20 and the triangular wave generation circuit 21.
(triangular wave W shown in FIG. 2a). The comparator 22 to which the reference voltage Vref and the triangular wave W are supplied has a triangular wave Wt with a period T - a pulse width t shown in FIG. 2bK, depending on the level of the reference voltage Vref. N pulse P
The switch 30 is modulated by this pulse P, for example, when the logic Jl of the pulse P is, the contact piece 30r is changed to the contact point 30a.
When the pulse P is logic '06, the contact 30r is switched to the contact 30b side and driven to provide the ground level to the active filter circuit 4G. . Active filter circuit 4
0 is the duty ratio D(
V according to D==+toN/T). , =D@V1 is rectified, smoothed, and converted into direct current, and at the same time, a gain of K times is given, and an output voltage of @D-vl is outputted to vo=.

Note that the duty ratio is θ˜1, which also indicates resolution, and by dividing and setting this duty ratio in the duty ratio setting means 10, a finely tuned gain can be obtained.

Since the programmable gain amplifier of the present invention is configured as described above, it can be configured with a small number of components such as switches and resistors, and a highly accurate gain can be obtained. Further, since the duty ratio can be set finely and easily by the duty ratio setting means 10, it is possible to subdivide the gain.

FIG. 3 is a circuit diagram showing only a filter circuit according to another embodiment of the present invention. Reference numeral 50 indicates a filter circuit, which is composed of a passive filter circuit 51 and an amplifier circuit 52. The passive filter circuit 51 includes resistors R,,R, and a capacitor c.
,,c,. The amplifier circuit 52 includes an operational amplifier 1, resistors 3f, and Rs.

Even if the filter circuit 50 having the configuration shown in FIG. 3 is replaced with the active filter circuit 40 shown in FIG. 1, the operation is similar to that of the embodiment shown in FIG. 1, and the same effect can be obtained.

In the above embodiment, the pulse width modulation circuit 20 is composed of a triangular wave generation circuit 21 and an amparator 22.
It may also be configured with a comparator. Although the switch 31 is shown as the gate means, it may be a chopper circuit or the like that functions similarly.

〔Effect of the invention〕

As explained above, the programmer map Jv11 of the present invention
The gain amplifier modulates the pulse width with the output of the duty ratio setting means. The input voltage is inputted into the filter circuit via the gate means in accordance with the duty ratio of the pulse output from the pulse width modulation means, and the pulse width is modulated by the output of the duty ratio setting means. Since it is configured to amplify, it can be configured with a small number of parts and the gain can be made highly accurate. Further, since the duty ratio can be set finely and easily by the duty ratio setting means, it is possible to subdivide the gay/gay ratio.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a programmable gain amplifier according to an embodiment of the present invention, @ Fig. 2 is a waveform diagram for explaining CFi operation, and Fig. 3 is a filter showing another embodiment of the invention. FIG. 4 is a circuit diagram showing a conventional amplifier. In the figure, 1 is an operational amplifier, 10 is a duty ratio setting means,
20 is a pulse width modulation circuit, 21 is a triangular wave generation circuit, 22
is a comparator, 30 is a switch, 40 is an active filter circuit, vl is an input voltage, and v. indicates the output voltage. Patent applicant: Yamatake Honeywell Co., Ltd. Figure 1, 40

Claims (1)

[Claims] a duty ratio setting means; a pulse width modulation means for modulating the pulse width by the output of the duty ratio setting means;
The gate means takes in an input voltage according to the duty ratio of the pulse output from the pulse width modulation means, and the filter circuit amplifies the input voltage taken in by the gate means with a predetermined gain to obtain an output voltage. Programmable gain amplifier.