JPH07321767A - Agc circuit - Google Patents

Abstract

PURPOSE:To restore an AGC control voltage level to a steady-state in a short time when the transmission mode is switched into the reception mode by throwing a sample-and-hold circuit to the position of sampling in the reception mode and throwing the sample-and-hold circuit to the position of holding in the spread spectrum radio equipment of the direct spread system. CONSTITUTION:A communication control section 14 provides the output of, e.g. an H level as a receiver side switching control signal in the reception mode, a transmission reception changeover switch 2 is thrown to the position of the reception to set a sample-and-hold circuit 18 in an AGC loop to the sampling position. In the case of transmission, a transmission reception switching signal outputted from the communication control section 14 goes to an L level to throw the transmission reception changeover switch 2 to the position of transmission and a transmission signal amplified by a power amplifier 5 is sent from an antenna 1 and the sample-and-hold circuit 18 is thrown to the position of holding to hold an AGC control voltage level in the reception mode. When the reception mode is selected again, the output of the sample-and-hold circuit 18 is held to a stable level at the preceding reception mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct sequence spread spectrum radio communication receiver, and more particularly to speeding up the AGC circuit of the receiver.

[0002]

2. Description of the Related Art In a conventional AGC circuit, as shown in FIG. 3, AGC amplifiers 7 and 10 capable of varying the gain of the amplifier are provided in an RF stage and an IF stage, and a correlation detector 13 is provided.
The demodulated data is extracted from the correlation signal detected by the data demodulator 13 and the output of the correlation signal of the correlation detector 13 is detected by the detector 15 to obtain the voltage level converter 16
The gain control signal converted to a predetermined level by the loop filter 17 is applied to the gain control terminals 19 and 20 of the RF amplifier 7 and the IF amplifier 10 to control the gain of the AGC. With the above configuration, the amplitude of the correlation output signal is detected, and only the signal for which correlation is obtained is detected to detect the AGC.
As shown in FIG. 4, the electric field strength input from the antenna at the time of reception fluctuates as shown by curves 31 and 32 due to a decrease in electric field strength due to fluctuations in communication distance, fading, etc. However, even if the input signal level from the antenna fluctuates along with this, an AGC loop that can keep the outputs of the amplifiers in the RF stage and the IF stage constant is configured. However, when the AGC circuit having the above-described configuration is used for a half-duplex bidirectional communication type radio device that needs to switch between transmission and reception, when the reception circuit shifts from the reception state to the transmission state, the reception circuit Since there is no signal input to the
The control voltage becomes indefinite, and as shown in FIG.
For example, when the control voltage becomes low and becomes the receiving state again, it takes a relatively long time for the AGC control voltage to rise to a predetermined level due to the time constant of the loop filter 17 or the like inserted in the circuit. It had a problem of cost.

[0003]

As described above, in the conventional half-duplex two-way communication type wireless device, the AGC control voltage becomes uncertain when transitioning from the reception state to the transmission state, and the reception is performed again. In this case, it takes a relatively long time for the AGC control voltage to return to a predetermined level due to the influence of a loop filter or the like in the circuit, and there is a problem that it is difficult to talk during this time. An object of the present invention is to provide an AGC circuit that enables the AGC control voltage level to return to a steady state in a short time when switching from transmission to reception.

[0004]

In order to solve the above problems, the present invention solves the above-mentioned problems by using an RF amplifier for amplifying a received signal, a mixer for mixing an output of the RF amplifier and an output of a local oscillator, and the mixer of the mixer. An IF amplifier that amplifies the output, a low-pass filter that filters the output of the IF amplifier, a correlation detector that detects the correlation of the output of the low-pass filter, and outputs a correlation signal, and an output of the correlation detector. A detector for detecting, a voltage level converter for converting the output level of the detector, and a filter,
Depending on the output of the filter, the RF amplifier and I
In a direct spread spectrum spread radio apparatus in which the gain of an F amplifier is controlled, a sample / hold circuit connected to the output of the voltage level converter is provided, and the output of the sample / hold circuit is set to the R
It is inputted to the gain control terminals of the F amplifier and the IF amplifier, and the sample / hold circuit is set to the sample side during reception, and the sample / hold circuit is set to the hold side during transmission.

[0005]

With the above construction, the AG according to the present invention
The C circuit is configured such that the switching control signal of the transmission / reception changeover switch causes the sample / hold circuit to switch to the sample side for sampling during the reception period and to switch to the hold side for holding during the transmission period, and to receive during the transmission period. A during the period
It works to maintain the GC level.

[0006]

Embodiments of the AGC circuit according to the present invention will be described in detail with reference to the drawings. In FIG. 1, for reception and reception, the signal input from the antenna 1 is input to the common contact 3 of the transmission / reception changeover switch 2, and the reception changeover terminal 6 is set to RF.
Connected to the input of the AGC amplifier 7 for input, the output of the RF amplifier 7 is input to the mixer 9 connected to the local oscillator 8, the output of the mixer 9 is input to the AGC amplifier 10 for IF, and the bandpass filter 11 is passed. Input to the correlation detector 12, the output of the correlation detector 12 to the data demodulation unit 13, the input to the communication control unit 14, the output of the correlation detector 12 to the detector 15, and the output of the detector 15 Is input to the voltage level converter 16, the sample-hold circuit 18 through the loop filter 17, and the gain control terminals 19 and 20 of the RF AGC amplifier 7 and the IF AGC amplifier 10. At the time of transmission, the output of the transmission power amplifier 5 is input to the switching terminal 4 and transmitted from the antenna 1. The transmission / reception switching signal is output from the communication control unit 14 and input to the switching control terminal 21 of the switcher 2 and the switching control terminal 22 of the sample hold circuit 18.

Next, the operation of the AGC circuit according to the present invention will be described. In FIG. 1, at the time of reception, the signal received by the antenna 1 is amplified by the RF stage amplifier 7, mixed with the local oscillator 8 and converted into an IF frequency.
The IF amplifier 10 amplifies the signal converted to the IF frequency, passes it through a bandpass filter 11, filters it, detects a correlation by a correlation detector 12, and extracts it as data by a data demodulator 13. The communication control unit 14 is subjected to predetermined data processing, is detected by a wave detector 15, is level-converted by a voltage level converter 16, passes through a loop filter 17, and is a gain control terminal of an RF amplifier 7 and an IF amplifier 10. 19 and 20 to control the gains of the RF amplifier 7 and the IF amplifier 10. The transmission / reception switching signal output from the communication control unit 14 is input to the switching control terminal 21 of the switcher 2 and the control terminal 22 of the sample hold circuit 18, and at the time of reception, as a receiving side switching control signal, for example, H The level is output,
As a result, the transmission / reception changeover switch 2 becomes the receiving side and the AGC
The sample and hold circuit 18 of the loop is on the sample side.

At the time of transmission, the transmission / reception switching signal output from the communication control unit 14 is set to the L level, the transmission / reception switching switch 2 is set to the transmission side, the transmission signal amplified by the power amplifier 5 is transmitted from the antenna, and the sample hold circuit 17 is also provided. Becomes the hold side, and the AGC control voltage level at the time of reception is held. Therefore, the gain control terminals 19 and 20 of the RF amplifier 7 and the IF amplifier 10 are
There is no response to the signal level leaking to the receiving unit at the time of transmission, and when transitioning to the receiving state again, as shown in FIG. 2, the output of the sample hold circuit 18 is stable AGC control at the time of the previous reception. Hold at voltage level.

[0009]

As described above, if the present invention is used for half-duplex communication, the AGC control signal of the AGC circuit is sampled at the time of reception and held at the time of transmission, so that the transmission state is changed to the reception state. The time required for the control voltage level of the AGC circuit to stabilize after switching is shortened.
The waiting time until the GC circuit becomes stable can be shortened, and the communication speed can be increased.

[Brief description of drawings]

FIG. 1 is a block diagram of an AGC circuit according to the present invention.

FIG. 2 is an explanatory diagram of AGC response time according to the present invention.

FIG. 3 is a block diagram of a conventional AGC circuit.

FIG. 4 is an explanatory diagram of a conventional AGC response time.

[Explanation of symbols]

 1 Antenna 2 Switch 3 Contact 4 Terminal 5 Amplifier 6 Terminal 7 Amplifier 8 Oscillator 9 Mixer

Claims (1)

[Claims] 1. An RF amplifier for amplifying a received signal, a mixer for mixing an output of the RF amplifier and an output of a local oscillator, an IF amplifier for amplifying an output of the mixer, and an output of the IF amplifier. A low-pass filter that filters the output of the low-pass filter, a correlation detector that detects the correlation of the output of the low-pass filter, outputs a correlation signal, a detector that detects the output of the correlation detector, and an output level of the detector. It consists of a voltage level converter and a filter,
Depending on the output of the filter, the RF amplifier and I
In a direct spread spectrum spread radio apparatus in which the gain of an F amplifier is controlled, a sample / hold circuit connected to the output of the voltage level converter is provided, and the output of the sample / hold circuit is set to the R
It is inputted to the gain control terminals of the F amplifier and the IF amplifier, and the sample / hold circuit is set to the sample side during reception, and the sample / hold circuit is set to the hold side during transmission. AGC circuit.