JPH0779215B2 - Gain adjuster - Google Patents

Description

DETAILED DESCRIPTION [Overview] For example, the present invention relates to a PCM transmission device that performs mutual signal conversion between a telephone band signal and a PCM (Pulse Code Modulation) code.
More specifically, the present invention relates to a gain adjustment device that adjusts the gain of a signal when performing A / D conversion and D / A conversion.In a gain adjustment device that includes a coarse gain adjustment circuit and a fine gain adjustment circuit, A / D, D / With the aim of enabling the gain setting that maximizes the S / N characteristics while considering the overload level of the A converter, the coarse gain adjustment unit for the analog signal provides coarse gain in units of positive predetermined step values. After the adjustment is performed, A / D conversion is performed by the A / D conversion means, and fine gain adjustment is performed by the precision gain adjustment means for the output, and the A / D The conversion means has a smaller value than the desired setting gain value required to secure the maximum signal-to-noise ratio, and the value obtained by adding a predetermined step value to that value is larger than the desired setting gain value. Set so that coarse gain value to the coarse gain adjustment means, configured to have a gain setting means for setting the fine gain adjustment means the value obtained by subtracting the coarse gain value from the setting desired gain value as a precise gain value. Also, after fine gain adjustment is performed on the digital signal by the precision gain adjustment means, D / A conversion is performed by the D / A conversion means, and the output thereof is adjusted by the coarse gain adjustment means in units of positive predetermined step values. In the gain adjustment device of the system that performs coarse gain adjustment and outputs as an analog signal,
A conversion means has a larger value than the desired setting gain value required to secure the maximum signal-to-noise ratio, and the value obtained by subtracting a predetermined step value from that value is smaller than the desired setting gain value. The coarse gain value is set in the coarse gain adjusting means, and the gain setting means is provided to set the value obtained by subtracting the coarse gain value from the desired gain value to be set in the fine gain adjusting means as the fine gain value.

[Industrial application field]

The present invention is applicable to telephone band signals and PCM (Pules Code Modulatio).
n) For example, the present invention relates to a PCM transmission device that mutually performs signal conversion with a code, and more specifically, relates to a gain adjustment device that adjusts a signal gain when performing A / D conversion and D / A conversion.

[Conventional technology]

It is becoming mainstream to convert analog signals into digital signals for transmission.

In this case, A / which converts an analog signal into a digital signal
D conversion technology and D / A conversion technology for converting digital signals into analog signals are indispensable. In A / D conversion and D / A conversion, it is necessary to perform conversion so that the signal-to-noise ratio (S / N, the same applies hereinafter) is as high as possible, and thus signal level adjustment is necessary.

For such level adjustment, the analog signal stage (A / D
What is done at the input side to the converter and the output side from the D / A converter) and what is done at the stage of the digital signal (output side from the A / D converter and input side to the D / A converter) There is.

The level adjustment at the stage of the digital signal can be performed only by the process of multiplying the constant corresponding to the level change, but it is difficult to perform the level adjustment entirely in the digital region due to the S / N characteristic. That is, for example, when a very low level signal is first converted into a digital signal by the A / D converter and the signal is multiplied by a value greater than 1, it passes through the A / D converter. Since the analog signal level at this time is low, the S / N characteristic is significantly deteriorated. Because A / D,
This is because a certain amount of noise is always added when passing through the D / A converter. Therefore, in terms of noise, the signal level when passing through the A / D and D / A converters should be as high as possible.

On the other hand, A / D and D / A converters are called standard levels, and normally, at a level that is 3 dB or more higher than that level, conversion is not accurately performed and overload occurs.

Therefore, it is desirable that the level passing through the A / D and D / A converters is as constant as possible. For example, in a system that performs audio signal processing with the A / D and D / A converters and the digital signal processing LSI. In this case, it is generally considered that a coarse level setting of, for example, 3 dB or 4 dB step is set in the analog domain, and a fine level setting lower than that is processed in the digital domain.

As an example of the level adjustment circuit at the analog stage, one that switches and uses a constant resistance type resistance network such as 0.1 dB, 0.2 dB, 0.4 dB, 0.8 dB, 1.6 dB, in which loss is doubled, or an operational amplifier is used. There is a method of changing the gain of the amplifier by switching the resistance.

[Problems to be Solved by the Invention]

However, conventionally, as described above, although there is a technique for performing level adjustment by sharing the coarse gain adjustment in the analog stage and the fine gain adjustment in the digital stage, the gain in the coarse gain adjustment and the gain in the fine gain adjustment are However, there is a problem in that a technique for optimizing the S so that the S / N characteristic is maximized in the range where overload does not occur has not been clarified.

For example, consider a case where the gain step width that can be set in the coarse gain adjustment circuit is 4 dB, and the standard level involving the overload level of the A / D and D / A converter is 0 dBm. In this case, if you want to add a gain of -15 dB, the gain of the coarse gain adjustment circuit on the A / D converter side should be set to -16 dB, and the coarse gain adjustment circuit on the D / A converter side should be set to -12 dB. It was completely unknown that it should be set.

INDUSTRIAL APPLICABILITY The present invention, in a gain adjusting device including a coarse gain adjusting circuit and a fine gain adjusting circuit, enables gain setting that maximizes the S / N characteristic while considering the overload level of the A / D and D / A converters. The purpose is to do.

[Means for Solving the Problems]

 1 (a) and 1 (b) are block diagrams of the present invention.

First, the configuration of the first aspect of the present invention is shown in FIG.
In this mode, after the coarse gain adjustment unit 102 performs coarse gain adjustment in positive predetermined step value units on the analog signal 101, the A / D conversion unit 103 performs A / D conversion, and the output thereof is It is premised on a system in which fine gain adjustment means 104 performs fine gain adjustment and outputs as a digital signal 105.

Further, it has the following gain setting means 106. That is, the same means has a value smaller than the desired setting gain value 109 required to secure the maximum signal-to-noise ratio in the A / D conversion means 103, and a value obtained by adding a predetermined step value to that value. The coarse gain value 107 is set in the coarse gain adjusting means 102 so that the value becomes larger than the desired set gain value 109. Then, the gain setting means 106 sets the value obtained by subtracting the coarse gain value 107 from the desired setting gain value 109 as the fine gain value 108 in the fine gain adjusting means 104.

Specifically, now, the coarse gain adjusting means 102 sets i to 1 ≦ i ≦
n is an integer that satisfies −LdB, −2LdB, ..., −2 ^i-1
・ Assume that ²ⁿ ways of gain adjustment are performed by combining n-attenuators of LdB, ..., −2 ^n-1 · LdB. Then, the gain setting means 106 repeats the following operations while sequentially reducing the value of the integer i from n to 1.

The desired gain value x (dB) and-(2) which are negative values required to secure the maximum signal-to-noise ratio in the A / D conversion means 103.
ⁱ⁻ 1−1) · L (dB) is compared.

As a result of this comparison, when x <−2 (2 ⁱ⁻¹ −1) · L, a process of setting a value obtained by adding 2 ⁱ⁻¹ · L to x as a new value of x is performed. At the same time, with respect to the coarse gain adjusting means 102, −2
Perform processing to connect an ^n-1 · L (dB) attenuator.

As a result of the above comparison, when x ≧ − (2 ⁱ⁻¹ −1) · L, no processing is performed.

By repeating the above operations, the combination of attenuators is set for the coarse gain adjusting means 102. Then, the gain setting means 106 sets a gain value equal to the value of x to the precision gain adjusting means 104 when the above-mentioned operation is completed.

Next, the configuration of the second aspect of the present invention is shown in FIG. In this mode, the fine gain adjustment means 111 performs fine gain adjustment on the digital signal 110, and then the D / A
It is assumed that the conversion unit 112 performs D / A conversion, the coarse gain adjustment unit 113 performs coarse gain adjustment in units of a predetermined positive step value on the output, and outputs the analog signal 114.

Further, it has the following gain setting means 115. That is, the same means compares the coarse gain value 117, which is the gain value in the coarse gain adjusting means 113, with the desired setting gain value 118 required for ensuring the maximum signal-to-noise ratio in the D / A converting means 112. The coarse gain value 117 is set to the coarse gain adjusting means 113 so that the coarse gain value 117 is large and the value obtained by subtracting the predetermined step value from the coarse gain value 117 is smaller than the desired set gain value 118. Then, the gain setting means 115 adjusts the precision gain value 116 such that the precision gain value 116, which is the gain value in the precision gain adjusting means 111, is the value obtained by subtracting the coarse gain value 117 from the desired setting gain value 118. The means 111 is set.

Specifically, now, the coarse gain adjusting means 102 sets i to 1 ≦ i ≦
n is an integer that satisfies −LdB, −2LdB, ..., −2 ^i-1
・ Assume that ²ⁿ ways of gain adjustment are performed by combining n kinds of attenuators of LdB, ..., −2n ^-1 · LdB. Then, the gain setting means 106 repeats the following operations while sequentially reducing the value of the integer i from n to 1.

The desired gain value x (dB), which is a negative value required to secure the maximum signal-to-noise ratio in the D / A conversion means 112, and −2 ^i-1
・ Compare with L (dB).

As a result of this comparison, when x ≦ −2 ⁱ⁻¹ · L, 2 ^{i−1 is set to} x.
-The value to which L is added is processed as a new value of x. At the same time, with respect to the coarse gain adjusting means 113, −2 ^n-1 · L (dB)
Perform the process to connect the attenuator of.

As a result of the above comparison, when x> − (2 ⁱ⁻¹ −1) · L, no processing is performed.

The combination of attenuators is set for the coarse gain adjusting means 113 by repeating the above differences. And
The gain setting means 115 displays x when the above operation is completed.
A gain value equal to the value of is set for the precision gain adjusting means 111.

[Action]

In the first mode of the present invention, the gain at the output of the coarse gain adjusting means 102 must be made smaller than the standard level of the A / D converting means 103 so as not to overload. Therefore, the gain setting means 106 makes the coarse gain value 107 set for the coarse gain adjusting means 102 smaller than the desired set gain value 109. Then, the analog signal that has passed through the coarse gain adjusting means 102 with such settings is
A / D conversion is performed by the / D conversion means 103, the precision gain value 108 by the precision gain adjustment means 104 is made a larger value, and the desired gain value 109 is set as a whole.

Further, in the second aspect of the present invention, since the coarse level adjusting means 113 is connected after D / A conversion, the gain setting means 115 is
The precision gain value 116 in the precision gain adjusting means 111 is made small so as not to exceed the standard level in the D / A converting means 112 to prevent the occurrence of overload. Then, the D / A conversion means 112 D / A converts the digital signal that has passed through the precision gain adjustment means 111 thus set, and the coarse gain adjustment means 113 sets the coarse gain value 117 to the desired gain value. Set a larger value than 118, and set the desired gain value as a whole 11
Set to 8.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of a PCM channel unit according to the present invention.

The analog transmission signal from the subscriber input from the analog transmission cable 201 is input to the coarse gain adjustment circuit 203 on the reception side via the transformer 202, where the amplitude of the analog transmission signal is coarse, such as 4 dB or 8 dB. Adjusted. The output is converted into a digital transmission signal by the A / D converter 204, and then a digital signal processor (DSP,
The same shall apply hereafter) 205. Then, the precision gain adjusting unit 206 in the DSP 205 finely adjusts the digital transmission signal. Then, the digital transmission signal whose gain has been adjusted by the precision gain adjustment unit 206 is subjected to digital signal processing such as equalization processing, and then the PC
Converted to M signal, PCM is sent to a multiplexer not shown.
It is transmitted as a transmission signal 207.

On the other hand, on the PCM line side, P
The PCM signal input to the DSP 205 as the CM reception signal 208 is converted into a digital reception signal in a format capable of digital signal processing and subjected to necessary digital signal processing such as equalization processing, and then to the precision gain adjusting unit 209. Then, the same fine gain adjustment as in the precision gain adjusting unit 206 is performed here. Then, the digital reception signal output from the precision gain adjustment unit 206 is output from the DSP 205 to the D / A converter 211, where it is converted into an analog signal and then input to the coarse gain adjustment circuit 212. Here, the coarse gain adjustment circuit 203
A coarse gain adjustment similar to is performed. Then, the output is output to the analog reception cable 214 via the transformer 213 and sent to the subscriber.

In addition to the above configuration, the gains in the coarse gain adjusting circuits 203 and 212 and the fine gain adjusting units 206 and 209 are optimally set by the gain setting unit 210 in the DSP 205. The gain setting algorithm in this portion is the most characteristic of this embodiment.

The precision gain adjusting units 206 and 209 and the gain setting unit 210
Is implemented as a combination of the hardware of DSP 205 and a microprogram for operating it.

Here, the coarse gain adjustment circuit 203 or 212 includes resistors R _{1 to} R ₆ and operational amplifiers OP ₁ and OP ₂ as shown in FIG. 3, for example.
Etc., and the switches S ₁ and S ₂ are controlled to be opened and closed to perform level adjustment such as 4 dB, 8 dB, ....

The gain setting unit in the DSP 205 in the embodiment having the above configuration
The gain setting operation by 210 will be sequentially described.

First, a first embodiment of the gain setting operation on the transmitting side (A / D converter side) for the coarse gain adjusting circuit 203 and the fine gain adjusting section 206, which is executed in the gain setting section 210, will be described.

Here, the coarse gain adjustment circuit 203 sets the coarse gain adjustment step to Ld by setting the coarse gain adjustment step to LdB.
It is assumed that gain adjustment is performed by combining n kinds of attenuators of B, 2LdB, 4LdB, ..., ^2n-1 · LdB.

Furthermore, the standard level of the A / D converter is set to 0 dBm. At this time, the input level of the A / D converter is optimal between -LdBm and 0dBm from the viewpoint of overload level and S / N characteristics (3dB margin for overload level is a system It must always be secured, and here it is considered overloaded when it exceeds 0 dB).

Further, in the coarse gain adjustment circuit 203, the gain that can be set by inserting or not inserting the above-mentioned n kinds of attenuators is 2 ⁿ kinds from 0 dB to − (2 ⁿ −1) · L dB in LdB steps. .

To make the explanation easier to understand, FIG. 4 shows an operation flowchart of the first embodiment of the gain setting operation on the transmission side, which is executed in the gain setting unit 210 when n = 3. When n = 3, in the coarse gain adjustment circuit 203, L
0dB, -LdB, -2LdB, -3LdB, -4LdB, depending on whether or not to insert three kinds of attenuators of dB, 2LdB, 4LdB respectively.
Eight coarse gain settings of -5LdB, -6LdB, and -7LdB are possible.

Now, when converting an analog transmission signal input from the analog transmission cable 201 into a digital transmission signal and outputting it to the PCM transmission cable 207, it is assumed that a gain setting value of xdB (negative value) is required as a whole. Is set in the gain setting unit 210 (S401). Note that this gain setting value is detected by a processing unit (not shown).

When the gain setting value xdB is set, first, in the coarse gain adjustment circuit 203, in order to determine whether to insert the 4LdB attenuator, the level is -3LdB higher than -4LdB.
LdB (generally equivalent to − (2 ⁿ⁻¹ −1) · LdB) is compared with x (S402).

If x is smaller, the coarse gain adjustment circuit 20
In 3, we decided to insert a 4 LdB attenuator (S40
3), and add 4L to x and set it as new x (S40
Four).

When x is larger, the 4 LdB attenuator is not inserted and no processing is performed.

Then, in the coarse gain adjustment circuit 203, in order to determine whether to insert an attenuator of 2LdB, LdB rather than -2LdB
High level -LdB (generally-(2 ^n-2 -1)
-Compare x with (equivalent to LdB) (S405).

If x is smaller, the coarse gain adjustment circuit 20
In 3, we decided to insert a 2 LdB attenuator (S40
6) Furthermore, add 2L to x and set it as new x (S40
7).

When x is larger, a 2 LdB attenuator is not inserted and no processing is performed.

Further subsequently, in the coarse gain adjustment circuit 203, in order to determine whether or not to insert an LdB attenuator, LdB rather than -LdB
High level 0 dB (generally − (2 ⁿ⁻³ −1) · L
(corresponding to dB) and x are compared (S408).

If x is smaller, the coarse gain adjustment circuit 20
In 3, we decided to insert an LdB attenuator (S409),
Further, a value obtained by adding L to x is newly set as x (S410).

When x is larger, the LdB attenuator is not inserted and no processing is performed.

Since the sum of the set values of the attenuator (negative value because it is considered as a gain) by the processing of steps S402 to S408 is always smaller than the initial gain setting value x, x after the processing based on the determination of S408 is positive. It is a value. Therefore, in S411, xdB amplification processing is set in the precision gain adjusting unit 206 (S411). Specifically, an antilogarithm equivalent to xdB is calculated, and the value is set as a multiplier in the multiplier that is the precision gain adjusting unit 206.

With the above gain settings on the transmission side, the coarse gain adjustment circuit 203
For example, in order to decide whether or not to insert an attenuator of 4 LdB, it is determined by whether it is larger or smaller than 3 LdB which is LdB smaller than that, and the desired gain x (positive value for amplification, negative value for attenuation) is set. Finally, x = gain (dB) of coarse gain adjustment circuit 203 + gain (dB) of fine gain adjustment unit 206 Gain (dB) of coarse gain adjustment circuit 203 ≦ x ≦ coarse gain adjustment circuit 203 Gain (dB) + L (dB) 0 ≦ gain (dB) ≦ L of the precision gain adjusting unit 206 can be satisfied.

As a result, the total gain in the coarse gain adjustment circuit 203 must be smaller than (a) desired setting gain x.

(B) It should be as large as possible.

Since the analog transmission signal is converted by the A / D converter 204 at the highest amplitude level without being overloaded, the highest S / N is obtained.

Next, as in the case of FIG. 4, when n = 3, it is executed by the gain setting unit 210. A first embodiment of the gain setting operation on the receiving side (D / A converter side) for the coarse gain adjusting circuit 212 and the fine gain adjusting section 209 will be described with reference to the operation flowchart of FIG. On the receiving side, the coarse gain adjustment circuit 212 is after the D / A converter 211, so the gain in the coarse gain adjustment circuit 209 is set to a larger value, and the corresponding amount of precision before the D / A converter 211 is increased. The gain adjusting unit 209 sets a negative gain (that is, attenuates it).
This operation is realized by the following operation flow.

First, when the gain setting value xdB is set (S501), first, in the coarse gain adjustment circuit 212, in order to determine whether to insert the 4LdB attenuator, -4LdB (generally,
(Corresponding to −2 ⁿ⁻¹ · LdB) and x are compared (S502).

If x is smaller, the coarse gain adjustment circuit 21
In 2, we decided to insert a 4 LdB attenuator (S50
3), then add 4L to x and set it as new x (S50
Four).

When x is larger, the 4 LdB attenuator is not inserted and no processing is performed.

Then, in the coarse gain adjustment circuit 203, in order to determine whether or not to insert a ² LdB attenuator, −2 LdB (generally equivalent to −2 ⁿ⁻² LdB) is compared with x ( S505).

If x is smaller, the coarse gain adjustment circuit 21
In 2, we decided to insert a 2 LdB attenuator (S50
6) Furthermore, add 2L to x and set it as new x (S50
7).

When x is larger, a 2 LdB attenuator is not inserted and no processing is performed.

Further subsequently, in the coarse gain adjustment circuit 203, −LdB (generally equivalent to −2 ⁿ⁻³ LdB) is compared with x in order to determine whether to insert an LdB attenuator. (S508).

If x is smaller, the coarse gain adjustment circuit 21
In 2, we decided to insert an LdB attenuator (S509),
Further, a value obtained by adding L to x is newly set as x (S510).

When x is larger, the LdB attenuator is not inserted and no processing is performed.

Since the total of the attenuator setting amounts (negative values because they are considered as gains) by the processing of steps S502 to S508 is always larger than the initial gain setting value x, x after the processing based on the determination of S508 is negative. It is a value. Therefore, in S511, the xdB negative width process (actual process is the attenuation process) is set to the precision gain adjusting unit 209.

With the above gain settings on the receiving side, the coarse gain adjustment circuit 212
For example, in order to decide whether or not to insert a 4 LdB attenuator, by judging whether it is larger or smaller than the same value of 4 LdB, finally, for the desired gain x (negative value) to be set, x = coarse Gain (dB) of gain adjusting circuit 212 + gain (dB) of precision gain adjusting unit 209 Gain of coarse gain adjusting circuit 212 (dB) ≧ x ≧ gain (dB) of coarse gain adjusting circuit 212 −L −L ≦ precision gain It is possible to satisfy the gain (dB) ≦ 0 of the adjusting unit 209.

As a result, the total loss in the coarse gain adjustment circuit 212 must be smaller than (a) the magnitude (positive value) of the desired set gain x.

(B) It should be as large as possible.

Since the digital received signal is converted by the D / A converter 211 at the highest amplitude level without being overloaded, the highest S / N is obtained.

Next, FIG. 6 shows an operation flowchart of the second embodiment of the gain setting operation on the transmission side executed in the gain setting section 210. This is so that the operation flowchart of the first embodiment of FIG. 4 can be applied to any n.

In the figure, when the gain setting value xdB is set (S601), the value of the variable m is initialized to 0 (S602), and the value of m is sequentially incremented (S606).
It is determined whether or not the volume has become equal to or higher than mL (S604). And
If x is greater than or equal to −mL, an attenuator of −m · LdB is inserted in the coarse gain adjustment circuit 203, and at the same time,
The precision gain adjustment unit 206 performs precision gain adjustment of x + m · LdB (S605). Then, when the value of the variable m exceeds 2 ⁿ −1, the processing ends (S603 → 607).

According to the above second embodiment of the gain setting operation on the transmission side,
The optimum gain setting exactly the same as in the first embodiment is realized.

Further, FIG. 7 shows an operation flowchart of the second embodiment of the gain setting operation on the receiving side executed in the gain setting section 210. This is so that the operation flowchart of the first embodiment of FIG. 5 can be applied to any n.

In the figure, when the gain setting value xdB is set (S701), the value of the variable m is set to the initial value 0 (S702), and the value of m is sequentially incremented (S706).
It is determined whether or not it has become larger than mL (S704). If x becomes larger than −mL, an attenuator of − (m−1) · LdB is inserted in the coarse gain adjustment circuit 212, and at the same time, x + (m
-1) Perform precise LdB gain adjustment (S705).
Then, when the value of the variable m exceeds 2 ⁿ −1, the processing ends (S703 → S707).

According to the second embodiment of the gain setting operation on the receiving side,
The optimum gain setting exactly the same as in the first embodiment is realized.

According to the first or second embodiment of the gain setting operation on the transmitting side and the first or second embodiment of the gain setting operation on the receiving side in the gain setting unit 210, which are described above, FIG. 8 shows a specific example of the gain value distributed to the parts. Note that the case of L = 4 dB and n = 4 is shown.

In each of the embodiments described above, the A / D converter 204 and the D / A
The standard level of the converter 211 was set to 0 dBm, but this value is MdBm.
When it is (arbitrary level), it means that the reference has moved, so in the initial setting of the value of x in FIGS. 4 and 5, it is sufficient to perform the process x + M → x and shift it by MdB. Is clear.

〔The invention's effect〕

According to the present invention, since the gain setting means can optimally set the coarse gain value in the coarse gain adjusting means and the fine gain value in the fine gain adjusting means, the input in the A / D converting means or the D / A converting means Since the output level can be always set to the maximum value equal to or lower than the standard level, the signal-to-noise characteristic of the system can be kept in the best state without causing the overload phenomenon.

[Brief description of drawings]

FIG. 1 is a block diagram of the present invention, FIG. 2 is a configuration diagram of an embodiment of a PCM channel unit according to the present invention, FIG. 3 is a diagram showing an example of the configuration of a coarse gain adjusting circuit, and FIG. An operation flowchart of the first embodiment of the gain setting operation on the transmitting side, FIG. 5 is an operation flowchart of the first embodiment of the gain setting operation on the receiving side, and FIG. 6 is a gain setting operation of the transmitting side. Operation flowchart of the second embodiment, FIG. 7 is an operation flowchart of the second embodiment of the gain setting operation on the receiving side, and FIG. 8 is a diagram showing an example of gain distribution (L = 4 dB, n =
4). 101, 114 ... Analog signal, 102,113 ... Coarse gain adjusting means, 103 ... A / D converting means, 104,111 ... Fine gain adjusting means, 105,110 ... Digital signal, 106,115 ... Gain setting means, 107, 117 ... coarse gain value, 108, 116 ... fine gain value, 109, 118 ... desired setting gain value, 112 ... D / A conversion means.

Claims (4)

[Claims] 1. An analog signal (101) is coarsely adjusted by a coarse gain adjusting means (102) in units of positive predetermined step values, and then A / D converting means (103) performs A / D conversion. Precision gain adjustment means (10
4) finely adjust the gain and digital signal (1
In the gain adjusting device of the system for outputting as 05), the A / D conversion means (103) has a smaller value than the desired setting gain value (109) required to secure the maximum signal-to-noise ratio. A coarse gain value (107) such that a value obtained by adding the predetermined step value to the value becomes larger than the desired gain value (109) to be set, the coarse gain adjusting means (102)
And a value obtained by subtracting the coarse gain value (107) from the desired setting gain value (109) is set as a precision gain value (116), and the precision gain (108) is set to the precision gain adjusting means (1).
A gain adjusting device having a gain setting means (106) for setting to 04). 2. A digital signal (110) is finely adjusted by a precision gain adjusting means (111) and then D / A converted by a D / A converting means (112). A coarse gain adjusting unit (113) performs a coarse gain adjustment in units of a predetermined positive step value and outputs as an analog signal (114) in a system gain adjusting apparatus, wherein the D / A converting unit (112) has a maximum signal pair. It has a larger value than the desired setting gain value (118) required to secure the noise ratio, and the value obtained by subtracting the predetermined step value from that value is smaller than the desired setting gain value (118). Such a coarse gain value (117) is used as the coarse gain adjusting means (11
The gain setting means (115) is set to 3) and the value obtained by subtracting the coarse gain value (117) from the desired setting gain value (118) is set as the precision gain value (116) in the precision gain adjusting means (111). ) Is provided, The gain adjustment device characterized by the above-mentioned. 3. An analog signal is coarsely adjusted by a coarse gain adjusting means in units of a predetermined positive step value L (dB), and then A / D converting means is used to perform A / D conversion.
In the gain adjusting device of the system for finely adjusting the output by the fine gain adjusting means and outputting as a digital signal, the coarse gain adjusting means sets i to an integer satisfying 1 ≦ i ≦ n, and LdB, 2LdB・ ・ ・, −2 ^i-1・ LdB, ・ ・ ・, −2 ^n-1
・ A combination of n kinds of attenuators of LdB is used to perform 2 ⁿ kinds of gain adjustment, a connection combination of the attenuators is set for the coarse gain adjusting means, and a gain value is set for the precise gain adjusting means. The desired gain value x (which is a negative value necessary to secure the maximum signal-to-noise ratio in the A / D conversion means while sequentially reducing the value of the integer i from n to 1 by the gain setting means. dB) and − (2 ^i-1 −1) · L (dB) are compared, and x <
In the case of − (2 ⁱ⁻¹ −1) · L, a process of setting a value obtained by adding 2 ⁱ⁻¹ · L to x as a new value of x, and −2 ⁿ⁻ for the coarse gain adjusting means. ^The operation of connecting an attenuator of ¹ · L (dB) is performed, and no operation is performed when x ≧ (2 ⁱ⁻¹ −1) · L. And a gain setting unit that sets a gain value equal to the value of x when the operation is finished to the precision gain adjusting unit. . 4. A fine gain adjustment is made to a digital signal by a precision gain adjusting means, a D / A conversion is made to the digital signal by the D / A converting means, and a positive predetermined step is made to the output by the coarse gain adjusting means. In a gain adjusting device of a system that performs coarse gain adjustment in value units and outputs as an analog signal, the coarse gain adjusting means sets i to an integer satisfying 1 ≦ i ≦ n, and LdB, 2LdB, ..., −2. ^i-1・ LdB, ・ ・ ・, -2
^n-1 LdB attenuators are combined to perform ²ⁿ gain adjustments, the attenuator connection combination is set for the coarse gain adjusting means, and the gain is set for the precise gain adjusting means. Gain setting means for setting a value, which is a negative value required to secure the maximum signal-to-noise ratio in the D / A conversion means while sequentially reducing the value of the integer i from n to 1. The value x (dB) is compared with -2 ^i-1 · L (dB) and x ≤ -2 ^i-1
When the value is L, the value obtained by adding 2 ⁱ -1.L to x is set as a new value of x, and -2 ^{n-1 with} respect to the coarse gain adjusting means.
・ Perform processing to connect an attenuator of L (dB), x> (2
^i-1 -1) · L, no processing is repeated to set the combination of the attenuators with respect to the coarse gain adjusting means, and when the operation is completed, x of A gain adjusting device comprising: a gain setting unit that sets a gain value equal to a value to the precision gain adjusting unit.