JPH06177806A - Power sum fixed agc circuit - Google Patents

Abstract

PURPOSE:To efficiently perform automatic gain control (AGC) and the maximum ratio synthesization of diversity received waves. CONSTITUTION:Levels (logarithmic values) alpha1 and alpha2 of received waves A and B are detected by logarithmic amplifiers 108 and 109 and with these values as inputs, control signals C1 and C2, which are proportional to a received value level (true value) and fix the sum, are outputted from ROM 203 and 204. Then, AGC is performed by controlling variable attenuators 110 and 111 corresponding to these control signals. Since the amplification factors of respective received waves are proportional to the input levels, the maximum ratio synthesization can be performed by diversity synthesization weighted by the signal levels after the AGC.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant power sum automatic gain control circuit for a system for diversity combining reception.

[0002]

2. Description of the Related Art In land mobile communications, a reduction in received power due to fading and a deterioration in a code error rate due to waveform distortion occur. Therefore, improvements are made by an automatic gain control circuit and a diversity technique. FIG. 3 shows a part of a conventional receiving circuit in which such a fading countermeasure is taken. The received wave A received by space diversity,
Assuming that the center frequency of B (two waves in this case) is f0, this is respectively a bandpass filter (BPF) 30
The band is limited by 1, 302, and only the signal component is extracted. Subsequently, the frequency converters 303 and 304 respectively generate frequencies f1 and f1 + Δ from the local oscillators 305 and 306, respectively.
By taking the difference from the single frequency signal of f, the center frequency is f0-f
It is converted into an intermediate frequency signal of 1, f0- (f1 + Δf), and these are amplified by an automatic gain control circuit (AGC) 307. Here, the difference Δf between the transmission frequencies of the two local oscillators 305 and 306 is set so that the signal spectra of the two intermediate frequency signals do not overlap.

FIG. 4 is a block diagram showing the configuration of the automatic gain control circuit 307. The two inputs I1 and I2 are added as they are, amplified by the variable gain amplifier 401, and then divided by the signal distributor 402. . One of them is detected by the detection circuit 403, smoothed by the time constant circuit 404, and input signal I1 +
A signal proportional to the power of I2 is taken out. This signal is amplified by the DC amplifier 405 and then amplified by the variable gain amplifier 40.
Input to 1 to adjust the amplification factor of this amplifier. By this feedback circuit, the level of the output signal taken out from the signal distributor 402 is controlled so as to be constant above a certain threshold value of the input.

Returning to FIG. 3, the output of the variable gain control circuit 307 is divided into two, and the frequency converters 308 and 310, respectively.
Frequency f from local oscillators 309, 311 added to
2, the baseband signal a by a single frequency signal of f2-Δf,
converted to b. here

## EQU1 ## f0 = f1 + f2.

With the above structure, two frequency converters 30 are provided.
If 3 and 304 have almost the same configuration, since the amplifier for automatic gain control is shared, the noise generation amount can be regarded as the same in both signal paths, and the input point of the automatic gain control circuit 307 can be considered. The S / N ratios of the received waves A and B and the S / N ratios of the baseband signals a and b are substantially the same. On the other hand, as for diversity combining, maximum ratio combining with the best output S / N is usually used, and this maximum ratio combining is performed by multiplying each received wave by a weight proportional to the S / N ratio and adding. Therefore, if the noise power is the same for the two signals as described above, then the baseband signal a,
Maximum ratio combining can be performed by multiplying b by a coefficient proportional to their power.

[0006]

In the above-mentioned conventional technique, a local oscillator for converting a received wave to an intermediate frequency band and a local oscillator for converting an intermediate frequency to a baseband are used. It is necessary to provide one set for each,
It is disadvantageous in terms of downsizing and economy of the device. Further, the variable gain amplifier 401 in FIG. 4 needs to be a wide band amplifier that amplifies a wide band signal obtained by adding two signal bands, but it is not easy to change the gain of such a wide band amplifier in a wide range. Absent.

Therefore, if the automatic gain control circuit 307 is divided into two and automatic gain control is performed for each received wave, these drawbacks can be eliminated, but in this case, the received level of each received wave is different. And the level of each received wave after each automatic gain control is no longer proportional to their S / N ratio. That is, even if diversity combining is performed using a weight proportional to the baseband signal level, this weight is not proportional to the S / N ratio, so maximum ratio combining cannot be performed.

It is an object of the present invention to provide a constant power sum automatic gain control circuit which can perform maximum ratio combining by weighting in proportion to its output level and which does not require a variable gain amplifier having a wide band in particular.

[0009]

The above object is to provide a constant power sum automatic gain control circuit for amplifying each of a plurality of diversity-received received waves with an amplification factor according to the input level thereof. The level detection means for detecting the level of the received wave and the control signal of each received wave have a value in which the sum of the control signals is constant and which is proportional to the level of the received wave detected by the level detecting means. And a variable gain amplifier for amplifying each received wave with an amplification factor proportional to the corresponding control signal generated by the control signal generating means. Further, the control signal generating means is accessed by A / D converting means for digitizing the level of each of the detected received waves and the digitized level by the means. A read only memory which outputs a digital control signal corresponding to the serial control signals, is accomplished by a digital control signal output from the memory to configure and a D / A converting means for converting the analog value.

[0010]

Since the amplification factor of each reception wave is set to a value proportional to the reception level and the sum of the amplification factors is controlled to be constant, the level of each reception wave at the output of the automatic gain control circuit and its S / The ratio with the N ratio is constant for each received wave,
Therefore, if diversity combining is performed with a weight proportional to each received wave level at the output of the automatic gain control circuit, maximum ratio combining is performed. Further, the circuit can be simplified by using the read-only memory (ROM) for generating the control signal.

[0011]

EXAMPLES The present invention will be described in detail below with reference to examples. FIG. 1 shows an embodiment of the circuit of the present invention, and shows the case of performing space diversity reception of two waves as in the conventional example. In the figure, each of the received waves A and B has a center frequency f0, and a band pass filter (BP)
F) After being band-limited by 101 and 102, respectively, a single frequency signal of frequency f1 from one local oscillator 105 is converted by the frequency converters 103 and 104 into an intermediate frequency band signal of center frequency f0-f1. It Next, each signal in this intermediate frequency band is divided into two by signal distributors 106 and 107, one of which is logarithmic amplifier 108, 10.
It is amplified in 9 and input to the control unit 200. The logarithmic amplifiers (LOG Amps) 108 and 109 are 0 to -70d.
It converts the inputs P1 and P2 of about bm into voltage signals α1 and α2 of about 2 to 0 V proportional to their logarithmic value, that is, the decibel value, and has a role of an input level detector for controlling the amplification factor. ing. here

## EQU2 ## αi = klog Pi, i = 1, 2, k: a constant.

FIG. 2 shows the detailed structure of the control unit 200. The detected values α1 and α2 of the input level are the A / D converter 20.
1 and 202 are digitized into 8 bits and are transmitted to the ROM 20 via the buffer memories 210 and 211, respectively.
It is input as a read signal to 3,204. ROM
The signals read from 203 and 204 are respectively D / A
After being converted into an analog signal by the converters 205 and 206 and the time constant circuits 212 and 213, a buffer amplifier 214,
215 outputs the control signals C1 and C2. Here, the relationship between the control signals C1 and C2 and the inputs α1 and α2 is

## EQU00003 ## Values of the ROMs 203 and 204 are set so that C1 = P1 / (P1 + P2) C2 = P2 / (P1 + P2).

Returning to FIG. 1, when the control unit 200 outputs control signals C1 and C2 that change according to the input power, the control signals cause the variable attenuators (VCA) 110 and 11 to operate.
An attenuation factor of 1 is controlled and its output is proportional to the input power times the control signal. This output is then the amplifier 112,
The signal is amplified by 113 and is converted by the frequency converters 114 and 115 into a baseband by the single frequency signal of the frequency f2 from the local oscillator 116 to become baseband signals a and b. Here, it is assumed that the frequencies f1 and f2 satisfy the relationship of (Equation 1).

According to this embodiment, from (Equation 3)

Since C1 + C2 = 1 C1 / C2 = P1 / P2 holds, the power ratio of the baseband signals a and b is the same as that of the received wave, and the sum thereof is constant. Therefore, the levels of the baseband signals a and b are S of the received waves A and B, respectively.
Assuming that the / N ratio is represented, the maximum ratio combination can be performed by combining the two with weighting proportional to the level.

[0015]

According to the present invention, since the ROM for determining the control signal for the automatic gain control can be constructed by the IC, the circuit configuration becomes simple, and the automatic gain control and the diversity combining by the maximum ratio combining are used together. The reception system can be easily realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a constant power sum automatic gain control circuit of the present invention.

FIG. 2 is a detailed configuration diagram of a control unit in FIG.

FIG. 3 is a diagram showing a configuration example of a system in which conventional maximum diversity ratio combining and automatic gain control are used together.

4 is a configuration diagram of the automatic gain control circuit of FIG.

[Explanation of symbols]

 108 logarithmic amplifier 109 logarithmic amplifier 110 variable attenuator 111 variable attenuator 200 control unit 201 A / D converter 202 A / D converter 203 ROM 204 ROM 205 D / A converter 206 D / A converter

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Tetsuya Sasaki 2-3-3 Toranomon, Minato-ku, Tokyo Kokusai Electric Co., Ltd.

Claims (2)

[Claims] 1. A constant power sum automatic gain control circuit for amplifying each of a plurality of diversity-received received waves with an amplification factor according to an input level thereof for detecting the level of each received wave. Control signal generation for setting the level detection means and the control signal of each received wave so that the sum of the control signals is constant and has a value proportional to the level of the received wave detected by the level detection means. And a variable gain amplifying means for amplifying each received wave with an amplification factor proportional to the corresponding control signal generated by the control signal generating means. 2. The control signal generation means is an A / D conversion means for digitizing the level of each of the detected received waves, and the control signal is accessed by the digitized level by the means. 2. A read-only memory for outputting a corresponding digital control signal, and a D / A conversion means for converting the digital control signal output from the memory into an analog value. Automatic gain control circuit with constant power sum.