JPH0969740A - Automatic gain control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a closed loop system where the transient response is not affected by the received signal level and to improve the transient response characteristic and the stability by controlling the gain of a variable gain amplifier by the output of a divider which divides the output of a loop filter by the output of a 2nd level detector that detects the effective value of an input signal. SOLUTION: The input received signal is also supplied to a level detector 21 from an input terminal 11, and the effective value of the received signal is detected. A divider 22 is placed between the output side of a loop filter 17 and the control input side of a variable gain amplifier 12. Then the divider 22 divides the output of the filter 17 by the detection output of the detector 21, and this division result is supplied to the amplifier 12 as a gain control signal. Under such conditions, the transient response of a closed loop system has no relation with the received signal level. Thus the optimum transmission function of the filter 17 is decided in terms of the transient response characteristic and the stability. Then the gain can be satisfactorily controlled with improved transient response and higher stability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION It is desirable that the signal power used for demodulation processing of a general wireless communication device is as constant as possible (desired value) from the viewpoint of reception accuracy and the like. On the other hand, when there are a plurality of communication partner stations, the communication distance and the propagation path differ depending on the partner stations, and therefore the received signal level (power) also naturally differs.

The present invention relates to an automatic gain control circuit for controlling an amplification gain according to a received signal level and realizing stable demodulation processing.

[0003]

2. Description of the Related Art FIG. 3 schematically shows an example of a conventional automatic gain control circuit. The input signal from the input terminal 11 is amplified by the variable gain amplifier 12 with a gain proportional to the gain control signal and output to the output terminal 13, and the level detector 14
Supplied to The difference between the output signal level P _O detected by the level detector 14 and the target value (level) P _S from the terminal 15 is detected by the difference detector 16, and this difference (control deviation amount) is detected.
Is input to the loop filter 17. The output of the loop filter 17 is used as a gain control signal for the variable gain amplifier 1
Input to 2 and its output level is constant (= target level)
A closed loop is formed so that The presence / absence of an input signal at the input terminal 11 is detected by the carrier sense 18, and the input signal is detected by the detection output and initialized to an operating state in which the gain of the variable gain amplifier 12 is controlled while the input signal is not detected. The loop filter 17 is controlled to the state.

In the operating state in which the input signal is detected, the gain A of the variable gain amplifier 12 is A = K _A · G _C (1) K _A : gain constant [1 / power] G _C : gain control signal level [ Power]. Therefore, the output level P _{O with} respect to the level P _{I of the} input signal is P _O = K _A · G _C · P _I (2) On the other hand, as described above, the reception (input) signal level P _I differs depending on the partner station (transmission source), but the reception signal level P _I can be treated as a constant value in each communication. Therefore, the open loop transfer function of the variable gain amplifier 12 when the gain control signal level G _C is the input signal (variable) is K _A · P _I (3). (K _A and P _I are both constants) In view of the above points, FIG. 4 shows that the closed loop formed by the conventional automatic gain control circuit unifies the physical quantity (signal) to be handled with the signal level (power), and sets the target value. (P _S ) to the controlled variable (P _I ) are modeled by a transfer function block. That is, the difference between the output level P _O and the target value P _S is taken in the difference circuit 16, the difference output is supplied to the loop filter 17 of the transfer function F (s), and the output thereof is obtained by inputting the input signal P _I to the gain K _A. The output signal is obtained through the multiplying circuit 12. Therefore, the transfer function of this closed loop is (K _A · P _I · F (s)) / (1 + K _A · P _I · F (s)) (4).

For the transient response of the closed loop system when the state where there is no received signal is changed to the state where the signal is received (when the filter is changed from the initializing state to the operating state), the unit step is virtually input to the target value. You can know it. From the equation (4), the step response of this closed loop is P ₀ (s) = K _A · P _I · F (s) / ((1 + K _A · P _I · F (s)) · S) P ₀ (t) = L ⁻¹ {K _A · P _I · F (s) / ((1 + K _A · P _I · F (s)) · S)}.

In order to obtain a reception accuracy above a certain level, the transient response derived from the equation (5) must converge within a certain error range. Therefore, the desired reception accuracy cannot be obtained until the transient response converges, and the transmitter must send dummy data. From Equation (5), P ₀ (t) is a function of P _I , and generally, the smaller P _I is, the longer it takes to converge within a certain error range, and the larger P _I is, the closed loop system becomes. Becomes unstable.

Conventionally, F (s) is determined so that the closed loop system is stable even if there is the maximum designed input, and then the transient response when the designed minimum received input is present is evaluated. , The length of dummy data (transmission time) was determined.

[0008]

As described above, in the conventional automatic gain control circuit, since the transient response of the closed loop system is a function of the received signal level P _I , the transient response characteristic and stability of the system cause F Unable to determine (s) in a unified way. That is, the optimum F (s) differs depending on the received signal level. An object of the present invention is to provide an automatic gain control circuit which forms a closed loop system in which a transient response is not influenced by the received signal level P _I and which is excellent in transient response characteristics and stability.

[0009]

According to the present invention, in addition to the structure of a conventional automatic gain control circuit, a second level detector for knowing the effective value of an input signal is provided. A divider that divides the output of the loop filter by the output is provided, and the output of the divider controls the gain of the variable gain amplifier.

With this configuration, an automatic gain control circuit whose transient response is not influenced by the received signal level P _I is realized.

[0011]

FIG. 1 shows an embodiment of the present invention.
Parts corresponding to those in FIG. 3 are denoted by the same reference numerals. In the present invention, the input reception signal from the input terminal 11 is also branched and supplied to the level detector 21, and the effective value of the reception signal is detected. Further, a divider 22 is inserted between the output side of the loop filter 17 and the control input side of the variable gain amplifier 12, and the output of the loop filter 17 is divided by the detected output of the level detector 21 in the divider 22. The division result is supplied to the variable gain amplifier 12 as a gain control signal.

When the control closed loop in this case is modeled by a transfer function block, as shown in FIG. 2, the difference between the target value P _S and the output level P _O is F (s) o, K
_A value obtained by multiplying _A and P _I is divided by the input level P _I , and the result of the division is used as the output P _O. The step response of this closed loop is as follows.

P _O (s) = (K _A · P _I · (1 / P _I ) · F (s)) / {(1 + K _A · P _I · (1 / P _I ) · F (s)) · S} = (K _A · F (s)) / ((1 + K _A · F (s)) · S) P _O (t) = L ⁻¹ {K _A · F (s) / ((1 + K _A · F (s) .S))} From the above, in the case of the automatic gain control circuit of the present invention, the transient response of the closed loop system becomes independent of the received signal level P _I. Therefore, from the standpoint of transient response characteristics and stability, the optimum F
(s) can be determined, and as a result, stability is higher than before,
Gain control can also be performed well in the transient response, and therefore the required dummy data can be short, so efficient communication can be performed.

[0014]

As described above, the transient response of the automatic gain control circuit according to the present invention is irrelevant to the received signal level P _I, and is optimum for the transient response characteristic and stability.
It is possible to determine (s), and it is possible to realize an automatic gain control circuit that has relatively high stability as compared with the conventional configuration and has a short required dummy data (allows efficient communication).

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic gain control circuit according to the present invention.

FIG. 2 is a transfer function block of the automatic gain control circuit shown in FIG.

FIG. 3 is a block diagram showing a conventional automatic gain control circuit.

4 is a transfer function block of the automatic gain control circuit shown in FIG.

Claims (1)

[Claims] 1. An input signal is amplified by a variable gain amplifier, the level of the amplified output signal is detected by a level detector, and the difference between the detected level and a target value is detected by difference detection means,
The difference detection output is supplied to the loop filter, the gain control signal which is the output of the loop filter controls the gain of the variable gain amplifier so that the output of the difference detection means becomes zero, and the presence or absence of the input signal. Is detected by the input detection means, and when the detection is not obtained, the loop filter is controlled to the initial state by its output, in the automatic gain control circuit, a second level detector for detecting the effective value of the input signal, An automatic gain control circuit, comprising: a division unit that divides the output of the loop filter by the detection output of the second level detector and supplies the output to the variable gain amplifier as a gain control signal.