JPH01241908A - Agc circuit - Google Patents

Abstract

PURPOSE:To attain quick response and to increase the reception dynamic range largely by amplifying an output of a comparator circuit by a buffer amplifier, integrating the output and obtaining an AGC voltage from a capacitor of the integration circuit. CONSTITUTION:An output of a comparator circuit 1 which detects a signal received by a receiver, compares the obtained detection signal with a comparison level 2 and generates an output in response to the difference, is amplified by a buffer amplifier 3, its output is integrated by an integration circuit 4 and an AGC voltage is obtained from the capacitor of the integration circuit 4. Thus, the capacitor is charged rapidly independently of the level of the output of the comparator circuit 1. Thus, the AGC circuit is obtained, which has a fast response to a change in the electric field strength of a reception signal from a weak, intermediate electric field to a strong electric field and has a large reception dynamic range.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an AGC circuit, and more particularly, to an AGC circuit that has quick response to changes in electric field strength of a received signal and has a wide dynamic range. .

[Prior Art] In the conventional AGC circuit of a radio receiver, in order to quickly raise or lower the AGC voltage, the detected signal is compared with a reference level by a comparator 11, as shown in FIG. The voltage according to the comparison result is amplified by the amplifier 12, and the integrating circuit 1
In addition to 3, the AGC is connected to the terminal of the integrating capacitor 14.
Obtaining voltage.

In this circuit where the voltage obtained as a comparison result of the comparator 11 is simply amplified by the amplifier 12 and the capacitor 14 is charged to obtain the AGC voltage, the comparator 11
Only a current amplified by a certain magnification corresponding to the difference between the comparison voltage and the detected signal flows to the capacitor 14 as a charging current.

[Problem to be solved] In such an AGC circuit, rapid charging is performed when a detection signal larger than the comparison voltage is input, that is, when the received radio signal is in a medium or strong electric field. A
Although the responsiveness of GC is relatively good, in a weak electric field, the difference between the detection signal and the comparison voltage is small, so the comparator 13
The output voltage of the capacitor 14 becomes smaller, the charging current for the capacitor 14 that generates the AGC voltage decreases, and it takes time to charge the capacitor 14 to a predetermined AGC voltage. As a result, the responsiveness of AGC deteriorates.

In addition, when the dynamic range of amplification "a12" cannot be achieved in such an AGC circuit, A
It is also possible to discharge the GC voltage and perform the amplification operation by the amplifier 12 in a medium to strong electric field. In such a case, the charging voltage in the medium electric field will also become small, and the circuit that quickly charges the AGC voltage generation capacitor will not function sufficiently when the received radio wave changes from a weak electric field to a medium electric field. The AGC voltage rises slowly. Therefore, the responsiveness of the AGC is particularly poor in the switching state from a weak electric field to a medium electric field. For this reason, in a state where the electric field is weak or is switched from a weak electric field to a medium electric field, if tuning is performed quickly, a phenomenon occurs in which radio waves cannot be received, and a synthesizer tuner may not stop at the time of auto search.

The present invention is intended to solve the problems of the prior art, and aims to provide an AGC circuit that can quickly respond to changes in the electric field strength of a received signal and can have a wide reception dynamic range. shall be.

[Means for Solving the Problems] The AGC circuit of the present invention to achieve such an object detects a signal received by a receiving device, compares the obtained detected signal with a comparison level, and calculates the difference between these signals. It is equipped with a comparator circuit that generates an output according to the output signal, a buffer amplifier that receives the output signal of this comparator circuit, and an integrating circuit that has a capacitor that receives the output signal of this buffer amplifier. This is what you get as follows.

[Function] In this way, the output of the comparison circuit is amplified by the buffer amplifier, the output is integrated by the integration circuit, and the AGC voltage is obtained from the capacitor of the integration circuit, so regardless of the level of the output of the comparison circuit, the capacitor It can be charged quickly.

As a result, it is possible to realize an AGC circuit that has a quick response to changes in the electric field strength of a received signal from a weak electric field to a medium electric field to a strong electric field, and can have a wide reception dynamic range.

[Embodiment] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment to which the AGC circuit of the present invention is applied, and FIG. 2 is a block diagram showing an example of a specific circuit thereof.

In FIG. 1, lO is an AGC circuit, and 1 is
This comparator compares the detection signal obtained from the detection circuit 6 with the voltage from the comparison voltage generation circuit 2, and generates a voltage corresponding to the difference as its output.

The output signal of the comparator 1 is input to a buffer amplifier 3 consisting of a differential amplifier circuit with a feedback non-inverting output, and the output of the buffer amplifier 3 is supplied to an integrating circuit 4. is taken out.

In this way, by replacing the conventional amplifier with the buffer amplifier 3 receiving the comparison result voltage of the comparator 1, the output side of the buffer amplifier 3 operates to match the input voltage, and the integrating capacitor 5 is rapidly charged. be done. The charging operation is determined by the voltage transfer function of the buffer amplifier 3 and the time constant of the integrating circuit 4, regardless of the voltage level on the input side of the buffer amplifier 3.

As a result, the AGC voltage is generated in the capacitor 5 at a fast response speed without being affected by differences in the electric field strength of the received radio waves, such as a strong electric field, a medium electric field, and a weak electric field.

Here, a buffer amplifier using a differential amplifier circuit with a feedback type non-inverting output is used, but the voltage amplification factor g is g-1 or less, and the current amplification factor α is
It is sufficient to use a non-inverting amplifier circuit with a large value, or an amplifier that performs a so-called buffer operation.

FIG. 2 shows a specific example of an AGC circuit using a voltage differential A lower, which is a non-inverting amplifier with a voltage amplification factor of 1, as a special example of a buffer amplifier. , amplifier circuits 21 and 22.

The differential amplifier circuit 20 receives the detected signal 61 from the detection circuit 6 at one input side, and receives a comparison voltage serving as a comparison reference at the other input side. The respective outputs taken out from the diode-connected load transistors 20a and 2ob inserted into the collector side of each transistor of this differential amplifier circuit 20 are two balanced outputs 4F'' No. 4 whose phases are different by 180 degrees. These outputs are respectively input to transistors 21a and 21b of the amplifier circuit 21, which are current mirror-connected to the load transistors 20a and 20b, and are also input to the load transistors 20a and 20b, respectively.
It is also input to transistors 22a and 22b of the amplifier circuit 22, which are connected to transistors 22a and 20b in a current mirror manner.

In the amplifier circuit 21, one transistor 21 of current mirror-connected load transistors 21c and 21d inserted into the collectors of transistors 21a and 21b.
The output is taken out from the load c, and in the amplifier circuit 22, the -
- An output having a phase difference of 180 degrees from the above is taken out from the load of the transistor 22c. These outputs having different phases are output from a transistor 24a that constitutes a differential amplifier circuit.

24b base, each is manually powered.

Here, the differential amplification circuit composed of the transistors 24a and 24b constitutes an amplification circuit of the voltage follower 24, and the collectors of these transistors are provided with load transistors 24c and 21d connected in a current mirror. An output is taken from the load on the transistor 24c side and sent to the capacitor 26 via the resistor 25 inserted on the collector output side of the transistor 24a.

As a result, capacitor 26 is charged in accordance with this output. A feedback resistor 27 is connected between the resistor 25 and the base of the transistor 24a, and the electric charge of the capacitor 26 is transferred to the feedback resistor 27, a diode 28a forming a bias circuit on the base side of the transistor 24a, and the resistor 2.
It is discharged by the discharge path of the series circuit consisting of 9a.

Therefore, here, the integral operation of charging and discharging is performed by a circuit composed of the capacitor 26, the resistor 25, the diode 28a, and the resistor 29a. That is, these resistors 2
5.29a and the capacitor 26 form an integrating circuit, and the terminal voltage of the capacitor 26 becomes the AGC voltage.

Here, to explain the operation of the voltage follower 24, since the capacitor 26 is inserted, the voltage on the base side of the transistor 24a is higher than the voltage on the base side of the transistor 24b, which receives a detection signal of the opposite phase. However, an output corresponding to the difference in the rise appears on the collector side of the transistor 24a, which charges the capacitor 26 via the resistor 25. As a result, the voltage on the base side of the transistor 24a is operated to match the voltage on the base side of the transistor 24b.
A voltage follower operation is performed.

By the way, here, a transistor 31 for quick charging is inserted between both terminals of the resistor 25, and when a potential difference sufficient to turn on the transistor 31 occurs between both terminals of the resistor 25, the power supply voltage VCC From there, the capacitor 26 is rapidly charged via the transistor 31.

Note that the base of the transistor 24b that operates differentially in the voltage follower 24 is also provided with a series circuit consisting of a diode 28b and a resistor 29b that constitute a bias circuit, similarly to the base of the transistor 24a.

As described above, although a feedback type buffer amplifier or voltage follower constituted by a differential amplifier circuit is used in FIG. 2, the present invention is not limited to such backup.

The integrating circuit in this invention may be any circuit as long as it performs an integral operation on an input signal as shown in the embodiment, and may be any circuit that performs various integral operations in addition to a normal integrating circuit. It includes a circuit.

[Effects of the Invention] As can be understood from the following explanation, in this invention, the output of the comparator circuit is amplified by a buffer amplifier, the output is integrated by an integrator circuit, and the AGC voltage is output from the capacitor of the integrator circuit. By obtaining , the capacitor can be charged rapidly regardless of the output level of the comparator circuit.

As a result, it is possible to realize an AGC circuit that has a quick response to changes in the electric field strength of a received signal from a weak electric field to a medium electric field to a strong electric field, and can have a wide reception dynamic range.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment to which the AGC circuit of the present invention is applied, FIG. 2 is a block diagram showing a specific example of the circuit, and FIG. 3 is a block diagram of a conventional AGC circuit. be. 1... Comparator, 2... Comparison voltage generation circuit, 3
... Buffer amplifier, 4... Integrating circuit, 5... Capacitor, 10... AGC circuit. Special Applicant ROHM Co., Ltd. Agent Patent Attorney Nobu Kajiyama Kore Patent Attorney 10 Riki Yamamoto Fuji

Claims (1)

[Claims] (1) A comparison circuit that detects the signal received by the receiving device, compares the obtained detected signal with a comparison level, and generates an output according to the difference between them, and a buffer amplifier that receives the output signal of this comparison circuit. An AGC circuit comprising: an integrating circuit having a capacitor receiving an output signal of the buffer amplifier, and obtaining an AGC voltage at a terminal of the capacitor.