JPH0783281B2 - AGC circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention can be applied to an analog or digital / analog mixed receiver or communication device even when there is a strong input signal far exceeding the inherent dynamic range.
Quickly generate large gain reduction in the signal system,
It also relates to an AGC circuit that can suppress distortion of the signal system,
In particular, the present invention relates to an AGC circuit suitable for a mobile radio receiver in which the strength of an input signal changes significantly depending on the surrounding conditions.

[Prior Art] In the receiving system in the conventional radio communication device shown in FIG. 6, the radio waves received by the antenna are "high frequency amplification stage 10"-"mixer 11"-"intermediate frequency amplification stage 12"-"detection stage 13". Then, the AGC voltage obtained by rectifying the signal applied to the detection stage 13 and applied to the amplifying section at the previous stage performs a process of reducing the amplification degree that is inversely proportional to the magnitude of the AGC voltage.

As the reception strength of the radio wave is accompanied by strong input due to changes in reception conditions such as tunnel passage, movement from the plain to a hill with good reception conditions, between buildings, approaching the broadcasting station, etc. Try to increase the gain reduction by controlling with AGC voltage. However, this gain control has the fact that the input waveform is distorted even if the gain is lowered (see Fig. 5 [II]). The degree of gain reduction is usually 30 dB per amplification stage, which is not sufficient.

In addition, when this process is the forward AGC control, a large bias current is supplied to the amplification stage for AGC control, so that the condition worsening that causes an increase in current consumption occurs, especially in portable receivers and wireless devices. Is hard to ignore.

Alternatively, in the case of reverse AGC control, there is a case where the required gain reduction cannot be obtained unless the AGC voltage is reduced to a negative voltage. Therefore, a negative power supply circuit is prepared for this case, resulting in an expensive system.

[Problems to be Solved by the Invention] According to the present invention, in a mobile radio receiver, even when there is a strong input signal far exceeding the dynamic range peculiar to the signal system, the bias current of the amplification element increases. It is to obtain an AGC circuit that can obtain a large gain reduction together with an unnecessary configuration of a negative power supply circuit that has been used to obtain a necessary gain reduction as well as suppression of an increase in power consumption.

[Means for Solving the Problem] The present invention is an AGC circuit in which a filter for receiving a voltage corresponding to an input signal strength is connected to each of a front stage and a rear stage of a high frequency amplification stage.

The detailed configuration is as follows: a first filter that receives an input signal, a high-frequency amplification stage connected to the first filter, a second filter connected to the high-frequency amplification stage, and a second filter thereof. The mixer connected to the filter and the detection stage connected to the mixer and outputting the AGC voltage are provided, and the first filter and the second filter receive the voltage related to the AGC voltage and the magnitude of the voltage. It is configured so that the degree of tracking error changes in accordance with the above, and further, the AGC voltage from the detection stage is
When the input signal received by the high-frequency amplification stage via the first filter has a strong input exceeding the inherent dynamic range, a voltage corresponding to the strong input is applied to the first and second filters, and the first filter Is an AGC circuit configured to give a voltage preset to the first and second filters so that the receiving sensitivity is maximized when the input signal received by is other than the strong input.

The first and second filters described above are configured to include a voltage-electrostatic capacitance conversion element.

[Operation] When the input signal from the first filter is input to the high frequency amplification stage, if the input signal is a strong input exceeding a fixed dynamic range, a voltage corresponding to the strong input is applied to the first and second voltages. When the input signal is other than strong input, a preset voltage is applied to the first and second filters to maximize the reception sensitivity.

[Example] As shown in FIG. 1, the AGC circuit includes a filter 1 for receiving a weak signal from an antenna that captures radio waves, a high-frequency amplifier stage 2 connected to the filter 1 for high-frequency amplification of the weak signal, and a high-frequency wave. Filter 3 connected to amplification stage 2
A mixer 4 connected to a filter for frequency conversion, and a detection stage 5 connected to the mixer for detection and outputting an AGC voltage.

In addition, the filter 1 and the filter 3 are from the detection stage 5.
It is configured to receive a voltage obtained by amplifying the AGC voltage and change the degree of tracking error according to the magnitude of the voltage.

In addition, when the AGC voltage from the detection stage 5 is a strong input when the input signal received by the high frequency amplification stage 2 via the filter 1 exceeds the dynamic range peculiar to it, the voltage corresponding to the strong input is applied to the filter 1 and the filter. 3 is applied to the filters 1 and 3 so that the reception sensitivity is maximized when the input signal received by the filter 1 is other than the strong input.

As shown in FIG. 4, the AGC voltage of the feedback signal is inverted by the diode D1 having the parallel capacitor C1 and the resistor r1 and input to the operational amplifier 7. The reference voltage of the operational amplifier 7 connected to 8V is set to 1.1V by the voltage division of the resistors r2-r3. The operational amplifier 7 is off when the feedback input is 1.1 V or less, and outputs the power supply voltage of the operational amplifier 7 to hold the transistor 9 off.

When the feedback input exceeds 1.1V, the output of the operational amplifier 7 drops, and in response to this, the transistor 9 outputs the gain control signal S and inputs it to the filters 1 and 3.
The substance of the gain control signal S corresponds to the feedback input or the AGC voltage and is the AGC voltage change itself fed back to the filters 1 and 3.

Diode D3 is for backflow prevention, Zener diode ZD2 reduces the power supply voltage 8V by about 2V, and the actual output of operational amplifier 7 is 6V.
The balance is balanced to stabilize the operation of the transistor 9.

The capacitor potentials of the filters 1 and 3 which have received the change of the AGC voltage from the feedback circuit change by this amount and shift the filter pass band, and a required and sufficient gain reduction is obtained. The bands of the filters 1 and 3 are tuned to the target frequency f ₀ except when the strong input is applied, and when the change in the AGC voltage corresponding to the strong input is fed back, the band is changed from FIG. 2 [A] to FIG. 2 [B]. , And the filter band shifts according to the feedback AGC voltage.

The relationship between the front end band and the gain shown in Fig. 3 is well known, and the reduction level a used as a filter is determined by the performance of the filter and the number of stages. In the case of the communication device of this example, it is about 60 to 80 dB. Is. The pass band shift voltage b required to obtain the remarkable maximum reduction a can be determined by the performance of the filter and the number of stages, and is about 3 V in the case of the communication device of this example. Therefore, in this example, by shifting the front end in the range of 0 to 3 V, it is possible to continuously obtain a gain reduction of 0 to 60 dB. The variable c in the figure is a value obtained by subtracting the filter loss (dB) from the gain (dB) of the amplification element.

FIG. 5 [I] shows the relationship between the AGC voltage V and the distortion d corresponding to the RF input of this example. The AGC voltage V is sufficiently controlled at 0 to 60 dB, and the fluctuation of the distortion d is also suppressed. . In the figure [I
[I] is an effective diagram of the conventional AGC circuit. Since the AGC voltage V also changes according to the magnitude of the RF input, the control cannot be said to be sufficient, and the distortion d largely changes without being suppressed. Same figure [III]
Is the AGC for the RF input without the feedback circuit
The relationship between the voltage V and the strain d is shown for reference.

[Advantages of the Invention] The gain control of the signal system by giving the AGC voltage change to the feedback circuit that gives the band tracking error of the high-frequency filter is sufficiently effective even for a stronger input region than the conventional one, and the AGC circuit concerned. Expand the strong input characteristics of.

Furthermore, when the AGC circuit of the present invention is used in a communication device, it is excellent in strong input characteristics and can keep the signal distortion in a high-sensitivity receiver at a minimum level, and a high-quality signal that suppresses distortion deterioration of the signal system. You can get the output. There is almost no increase in current consumption, and it is easy to attach to a conventional varicap tuned receiver. Moreover, it is used in a design that does not control the high frequency amplification element, so the operation stability of the amplification element is outstanding. Is.

Further, when the present invention is applied to a varicap tune type receiver, there is a great low cost merit that it can be implemented only by adding a feedback circuit composed of one operational amplifier.

[Brief description of drawings]

FIG. 1 is an electric block circuit diagram showing an embodiment of the present invention, and FIGS. 2A and 2B are graphs showing band shifts.
FIG. 3 is a graph showing a filter function, FIG. 4 is a circuit explanatory view showing an example of a feedback circuit, FIG. 5 [I],
[II] and [III] are graphs showing the characteristics by the feedback of the present invention, the characteristics of the conventional feedback, and the case without the feedback, respectively, and FIG. 6 is an electric circuit block diagram of the conventional communication device. 1, 3: Filter

Claims (1)

[Claims] 1. A first filter having a voltage-electrostatic capacitance conversion element for receiving an input signal, a high-frequency amplification stage connected to the first filter, and a voltage-electrostatic capacitance conversion element. A second filter connected to the high-frequency amplification stage, a mixer connected to the second filter, and an AGC connected to the mixer.
A detection stage that outputs a voltage is provided, and the first filter and the second filter are configured to receive the voltage related to the AGC voltage and change the degree of the tracking error according to the magnitude of the voltage. When the AGC voltage from the detection stage is a strong input in which the input signal received by the high frequency amplification stage via the first filter exceeds the dynamic range peculiar to the first filter, the voltages corresponding to the strong input are set to the first and second voltages. To the first filter, and the first preset voltage is set so that the receiving sensitivity becomes maximum when the input signal received by the first filter is other than strong input.
And an AGC circuit configured to feed the second filter, respectively.