JP3360622B2 - Volume gain test equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a volume gain tester for measuring a gain of an electronic volume or the like built in an IC.

As a volume circuit built in an IC,
It is known that an input resistance and a feedback resistance of an inverting amplifier are each switched by a switch element to obtain a predetermined attenuation rate. In this type of volume circuit, an amplitude ratio or an amplitude difference between input and output signals is obtained while sequentially changing the gain, and a volume gain test is performed by confirming whether a desired gain is obtained. .

[0003]

However, in the above-described volume circuit, if an attempt is made to obtain a large attenuation rate such as -80 dB or -90 dB, the output voltage becomes very small, so that the measurement is extremely difficult. There was a problem that a correct gain test could not be performed.

The present invention has been made in view of the above circumstances, and provides a volume gain test apparatus that can easily confirm whether a desired gain is obtained regardless of the gain of a volume circuit. The purpose is to:

[0005]

According to the present invention, there is provided a volume gain test apparatus incorporated in an IC together with a volume circuit for amplifying or attenuating an input signal for measuring a gain of the volume circuit, A correction volume circuit that is provided at an output stage of the volume circuit and amplifies or attenuates the output of the volume circuit; and when measuring the gain of the volume circuit, the gain of the correction volume circuit is defined as the gain of the volume circuit. A control means for setting the overall gain to approach 1, and setting the gain of the correction volume circuit to 1 during normal operation.

According to the present invention, at the time of the gain test, the gain of the correction volume circuit is set so that the overall gain including the volume circuit approaches 1, so that the input / output amplitude difference approaches 0. , And the amplitude ratio approaches 1.
This facilitates the gain test of the volume circuit.

In particular, the control means sets the gain of the correction volume circuit at the time of measuring the gain so that the total gain with the gain of the volume circuit becomes a first value, and then sets the overall value. When the gain is set to be the second value, the gain of either the volume circuit or the correction volume circuit can be determined from the expected value and the measured value of the first value, the second value, and the specified value. It is found out that it is off, and the test accuracy is further increased.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a main part of an IC incorporating a volume test apparatus according to one embodiment of the present invention. A correction volume circuit 2 is connected to the output stage of the volume circuit 1 to be tested, and the gains of the volume circuit 1 and the correction volume circuit 2 are switched by a controller 3. The correction volume circuit 2 and the controller 3 constitute a volume test apparatus of the present invention.

The volume circuit 1 comprises an inverting amplifier,
, R1n, a plurality of input resistors R11, R12,..., R1n connected in parallel to the inverting input terminal thereof, and switching elements T11, T12,. , R2n and switch elements T21, T22,..., T2n that switch between the feedback resistors R21, R22,. Similarly to the volume circuit 1, the correction volume circuit 2 is formed of an inverting amplifier,
, R3n connected in parallel to the inverting input terminal thereof, and switching elements T31, T32,..., T3n for switching between them, and the output terminal of the operational amplifier 11 and the inverting input terminal. , R4n connected in parallel between them and switch elements T41, T42,..., T4n for switching between them.

Now, resistors R11 to R1n, R21 to R2n, R31
FIG. 2 shows an equivalent circuit when the selected resistance values among R1 to R3n and R41 to R4n are R1, R2, R3, and R4, respectively. Here, the gain G1 of the volume circuit 1 and the gain G2 of the correction volume circuit 2 are respectively

[0011]

G1 = -R2 / R1 G2 = -R4 / R3

## EQU1 ## Therefore, the relationship between the input voltage Vi input to the volume circuit 1 and the output voltage Vo output from the correction volume circuit 2 is

[0013]

## EQU2 ## Vo = G1, G2, Vi = (R2 / R1).
(R4 / R3) Vi

## EQU1 ## G2 = 1 / G1 (that is, R4 / R
If 3 = R1 / R2, the total gain is 1 (= 0 dB). Therefore, for example, G1 = 0
dB to -90 dB (-5 dB steps), G2 = 0 dB
It can be varied in the range of +90 dB (+5 dB step). Then, at the time of the test, first, as a first step,
As shown in Table 1 below, the controller 3 changes the gains of the volume circuit 1 and the correction volume circuit 2 and checks the input and output.

[0015]

[Table 1]

Next, as a second step, the controller 3 changes the gains of the volume circuit 1 and the correction volume circuit 2 as shown in Table 2 below, and checks the input and output.

[0017]

[Table 2]

The order of the first step and the second step may be reversed. By performing measurement in at least two combinations in this manner, for example, the gain G1 of the volume circuit 1 is 0, -5, -10, -15, -20,..., And the gain G2 of the correction volume circuit 2 is 0, +5. , + 10, + 1
5, + 20, ..., where should be, volume circuit 1
Gain G1 of 0, -6, -12, -18, -24,
..., the gain of the correction volume G2 is 0, +6, +12,
.., +24,..., The total gain does not change at 0 dB in the first step alone, so that it cannot be detected that the gain deviates from the specified value. However, when the test of the second step is performed, the combined gain becomes 0, -6, -6, -6,..., So that the gain of either the volume circuit 1 or the correction volume circuit 2 is out of the specified value. It turns out. Moreover, the measured total gain is about 0 dB to -10 dB, which is a sufficiently measurable range, and the measurement is extremely easy.

On the other hand, during normal operation, the gain of the correction volume circuit 2 may be fixed to 0 dB at all times. This eliminates the need for special test terminals.

[0020]

As described above, according to the present invention, at the time of the gain test, the gain of the correction volume circuit is set so that the overall gain including the volume circuit is close to unity. This produces an effect that the output amplitude difference approaches zero, and the gain test of the volume circuit becomes extremely easy.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a main part of an IC incorporating a volume gain test apparatus according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an equivalent circuit at the time of testing the IC.

[Explanation of symbols]

1. volume circuit, 2. correction volume circuit, 3. controller.

Claims (2)

(57) [Claims] 1. A volume gain tester for measuring a gain of a volume circuit which is built in an IC together with a volume circuit for amplifying or attenuating an input signal, and is provided at an output stage of the volume circuit. A correction volume circuit that amplifies or attenuates the output of the volume circuit, and when measuring the gain of the volume circuit, the overall gain of the correction volume circuit and the gain of the volume circuit approaches 1. And a control means for setting the gain of the correction volume circuit to 1 during normal operation. 2. The control means sets the gain of the correction volume circuit at the time of measuring the gain so that the total gain with the gain of the volume circuit becomes a first value, and then sets the overall gain. 2. The volume gain test apparatus according to claim 1, wherein the gain is set so as to have a second value.