JPH0346826A - Communication equipment and agc circuit - Google Patents

Abstract

PURPOSE:To extend the strong input characteristic of an AGC circuit and to suppress the distortion degradation of a signal system by applying the change of the AGC voltage to a filter including a voltage/capacitance conversion element of a high frequency or intermediate frequency amplifier circuit and generating a band tracking error of the filter. CONSTITUTION:A weak signal of an antenna for a radio wave is inputted to a high frequency amplifier stage a through a filter 1 and amplified and inputted to an IF amplifier stage 5 from a filter and to a mixer 4 and amplified again and outputted from a detecting stage 6 to a speaker or the like. In this main circuit, the AGC voltage is taken out from the detecting stage 6 and fed back to filters 1 and 3. Filters 1 and 3 which receive the change of the AGC voltage through a feedback circuit shift the filter band pass characteristics to obtain required sufficient gain reduction. Bands of filters 1 and 3 are tuned to an objective frequency f0 except for a strong input; and when the change of the AGC voltage corresponding to the strong input is fed back, the bands of filters are shifted in accordance with the feedback AGC voltage to obtain greater gain reduction.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an analog or mixed digital/analog receiver or communication device that can operate even when there is a strong human input signal that far exceeds the inherent dynamic range.
Quickly generates large gain reduction in the signal system,
The present invention also relates to an AGC circuit that can suppress distortion in a signal system, and is particularly applicable to an AGC circuit suitable for a mobile radio receiving device in which the strength of a human signal changes significantly depending on the surrounding situation.

[Prior Art] In the receiving system of a conventional wireless communication device shown in FIG. 6, the radio waves received by the antenna are
Mixer 11J-r intermediate frequency amplification stage 12J-r detection stage 1
The AGC voltage obtained by rectifying the signal processed in 3' and applied to the detection stage 13 is applied to the amplification section in the previous stage, and the amplification degree is reduced in inverse proportion to the magnitude of the AGC voltage.

The reception strength of radio waves is affected by strong input times due to changes in reception conditions such as passing through a tunnel, moving from a plain to a hill with good reception conditions, between buildings, and approaching a broadcasting station. Trying to increase the gain reduction by controlling it with the AGC voltage. However, with this gain control, there is a fact that even if the gain is lowered, the manual waveform is distorted (see Fig. 5 [11]). The degree of gain reduction is usually 30 dB per amplification stage, which cannot be said to be sufficient.

Also, if this process is forward AGC control, the AGC
Since a large amount of bias N and current is applied to the amplification stage for control purposes, conditions deteriorate, leading to an increase in current consumption, and this deterioration of conditions is difficult to ignore, especially in portable receivers and radio equipment.

Alternatively, in the case of reverse AGC control, there are times when the necessary gain reduction cannot be obtained unless the AGC voltage is reduced to a negative voltage, resulting in an expensive system that requires a negative power supply circuit in preparation for such situations.

[Problems to be Solved by the Invention] The present invention solves the problem of increasing the bias current of the amplifying element even when there is a strong input signal that far exceeds the inherent dynamic range of the signal system in a receiving device for a mobile line. The object of the present invention is to suppress the accompanying increase in power consumption, eliminate the need for a negative power supply circuit that has been used to obtain the necessary gain reduction, and provide an AGC circuit that can obtain a large gain reduction.

[1ff! [Means for Solving the Problem] In a receiving device such as a mobile radio, instead of changing the bias of the input circuit of a high frequency amplification element (including an intermediate frequency amplification element) as in the past, changing the GC voltage to is added to a filter that includes a voltage-to-electrostatic capacitance conversion element in a high-frequency amplifier circuit or an intermediate-frequency amplifier circuit, and generates a band tracking error in the filter, thereby obtaining a large gain reduction.

[Operation and implementation 1'711] The communication device shown in the embodiment of FIGS. 1(A) and 1(B) manually amplifies a weak signal from an antenna that captures radio waves from a filter 1 to a high frequency amplification stage 2, From the filter 3 and mixer 4, it is manually amplified and processed again by the Il'' amplification stage 5, and then output from the detection stage 6 to a speaker, etc. The main circuit takes out the AGC voltage from the detection stage 6, and the AGC voltage is output from the detection stage 6. Cf
The ff pressure is fed back to filters 1 and 3.

Conventional main circuits of communication equipment, high frequency amplification stage 2, mixer 4,
The IF amplification stage 5 does not require any modification.

The embodiment shown in FIG. 1 [B] shows a case where the I l'' amplification stage 5 is not used, and a diode 8.8 is used in the feedback circuit to provide feedback/AG to the filters l and 3.
A means for strengthening the prevention of backflow of the C voltage is also shown.

As shown in FIG. 4, the feedback signal A
1 is inverted and input to operational amplifier 7. The reference voltage of the operational amplifier 7 connected to 8V is connected to the resistor r 2 - r 3
With a partial pressure of 1. Set to IV. The operational amplifier 7 has the feedback input 1. When it is OFF when it is below IV, the power supply voltage of the operational amplifier 7 is output and the transistor 9 is turned OFF.
Hold at F.

-H Note Feedback When the input voltage exceeds IV, the output of the operational amplifier 7 decreases, TIE is applied to this, and the transistor 9 outputs a gain control signal S, which is input to the filters 1 and 3. The substance of the gain control signal S corresponds to the feedback input or AGC voltage indicated by ``-'', and is the AGC voltage change itself that is fed back to the filters 1 and 3.

The diode F'D3 is for backflow prevention, and the Zener diode ZD2 is for backflow prevention and lowers the current R voltage of 8V by about 2cm to balance the actual output of the operational amplifier 7 of 6V and stabilize the operation of the transistor 9.

The capacitor potential of the filter 1.3, which has received a change in the AGC voltage from the feedback circuit, is converted to this degree to shift the filter pass band and obtain the required sufficient gain reduction. Except for strong input, the band of filter 1.3 is tuned to the target frequency "0", and the AG corresponding to strong input
When the change in the C voltage is fed back, it changes from FIG. 2 [A] to FIG. 2 [B], and a shift in the filter band occurs according to the feedback AGC voltage.

The relationship between the front end band and gain shown in Figure 3 is well known, and the reduction level a used as a filter is determined by the performance and number of stages of the filter, and in the case of the communication device in this example, it is approximately 60 to 80 dB. be. The passband shift voltage S required to obtain the noteworthy maximum reduction a can be determined by the performance and number of stages of the filter, and is approximately 3<1> in the case of the communication device of this example. Therefore, in this example, by shifting the front end in the range of θ to 3V, gain reduction of 0 to 60 dB can be obtained continuously. The variable C in the figure is the value obtained by subtracting the filter loss (dB) from the gain (dB) of the amplification element.

FIG. 5 [l] shows the relationship between the AGC voltage and the voltage distortion d corresponding to the RF manual power of this example, and the AGC voltage V is sufficiently controlled at 0 to 60 dB, and the variation in the distortion d is also suppressed. Figure [11] is an effective diagram of the conventional AGC circuit, and R
Since the AGC voltage V also changes according to the magnitude of the human power F, the control cannot be said to be sufficient, and the distortion d is not suppressed and changes greatly. [+11] in the same figure shows for reference the relationship between AGCm pressure V and strain d for RF human power in the case without a feedback circuit.

[Effects of the Invention] Gain control of the signal system, which applies AGC voltage changes to a feedback circuit that provides a band tracking error of a high-frequency filter, is sufficiently effective even in a stronger input region than before, and the AGC circuit concerned Expand the strong input characteristics of

Furthermore, the communication device of the present invention including the AGC circuit has the following features:
In addition to having excellent strong input characteristics, it is possible to keep signal distortion in a high-sensitivity receiver at a minimum level, and it is possible to obtain high-quality signal output with suppressed deterioration of distortion in the signal system. There is almost no increase in current consumption, and it is easy to install in conventional varicap tune receivers.Furthermore, the design does not require any control of the high-frequency amplification element, so the operation of the amplification element is extremely stable. It is.

Further, when the present invention is applied to a varicap tune receiver, there is a great advantage of low cost since it can be implemented simply by adding a feedback circuit consisting of one operational amplifier.

[Brief explanation of drawings]

Fig. 1 [A], CB] is an electrical block circuit diagram showing an embodiment of the present invention, Fig. 2 [A], [B] is a graph showing band shift, and Fig. 3 is a graph showing filter function. ,
FIG. 4 is a circuit explanatory diagram showing an example of a feedback circuit,
FIG. 5 [1], [11] and [11] show the characteristics by the feedback of the present invention, the characteristics of the conventional feedback,
The graphs show the cases without feedback, and FIG. 6 is an electric circuit block diagram of a conventional communication device. 1.3: Filter

Claims (1)

[Claims] 1) An AGC circuit that controls the gain of a signal system by applying changes in AGC voltage to a feedback circuit that provides a band tracking error of a high frequency filter. 2) A communication device characterized by comprising an AGC circuit having strong input characteristics that suppresses deterioration of distortion in a signal system by applying changes in the AGC circuit to a feedback circuit that gives a band tracking error of a high frequency filter.