JPS63236404A - Agc circuit - Google Patents

Abstract

PURPOSE:To realize miniaturization and low power consumption, by applying an AGC controlled voltage on the base of a transistor for amplification, and turning on/off a pin diode by the voltage drop of the collector. CONSTITUTION:A prescribed voltage is applied from a terminal 21 on the base of the transistor 1 in advance, and furthermore, an AGC voltage is applied on the base via a switching diode 13. The pin diode is turned on/off by the voltage drop due to the resistor 8 of the collector of the transistor 1. Consequently, it is possible to prevent the distortion characteristic of the transistor 1 for amplification from being deteriorated, and since the pin diode 5 is driven by using a part of a collector current which flows on the transistor 1, it is possible to realize the miniaturization and the low power consumption.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an AGC circuit, and particularly to an AGC circuit suitable for a television chainer or a satellite broadcast receiver 1 (JZ chicona).

[Conventional technology]

A typical conventional example of an AGC circuit used in a tuner is described in Japanese Patent Publication No. 56-107652. This is a circuit in which a type 1 AGC circuit is constructed using five pin diodes, and the gain is varied by applying an AGC control voltage to the pin diodes via a control transistor. This circuit requires a pin diode drive transistor in addition to the pin diode as an AGC circuit, which increases the size of the circuit. There were issues such as high current consumption.

[Problem that the invention seeks to solve]

In the above conventional technology, the collector current that drives the amplification transistor and the current that drives the pin diode are made independent, which increases the power consumption of the AGC circuit.Also, since a transistor for driving the pin diode is separately provided, the circuit becomes large. The problem was that the shape was complicated.

An object of the present invention is to use an amplification transistor as a pin diode drive transistor to reduce the size and power consumption of an AGC circuit.

[Means for solving problems]

In the present invention, the cathode of the collector diode of the amplification transistor is connected in series, a fixed bias is applied to the anode of the diode, and the current flowing through the diode is controlled by applying an AGC voltage to the base of the amplification transistor. control and achieve the above objectives. Here, a fixed bias is applied to the base so that a constant voltage is applied to the base of the transistor even when the AGC voltage becomes OV, and the AGC voltage is further applied to the base of the transistor via the switching diode. did.

[Effect]

The collector voltage of the amplification transistor is supplied to the cathode of the bin diode, and a fixed bias from the power supply is applied to the anode. When the AGC11C pressure applied to the base of the amplification transistor increases, the collector voltage of the transistor decreases, the bin diode turns on, and the amount of signal attenuation decreases. On the other hand, when the AGC voltage decreases, the collector voltage of the transistor increases, the current flowing through the bin diode decreases, and the amount of signal attenuation increases. When the collector voltage of the transistor becomes higher than the fixed voltage supplied to the anode of the Vin diode, the Vin diode is turned off and the amount of attenuation becomes maximum. Here, even when the AGC voltage applied to the base of the transistor becomes Or, it is necessary to apply a constant voltage to the base of the transistor in order not to deteriorate the distortion characteristics of the transistor. For this reason, in the present invention, a constant voltage is applied to the base in advance by resistance division from the power supply, and the AGC' voltage is further applied to the base via the switching diode. According to this method, when the AGC voltage is lower than the fixed bias of the base, the fixed bias is directly applied to the base, thereby preventing deterioration of the distortion characteristics of the amplification transistor.

〔Example〕

Hereinafter, the present invention will be explained in detail according to embodiments shown in the drawings. FIG. 1 shows an embodiment of the present invention. The AGC circuit of the present invention includes a high frequency amplification transistor 1, a bin diode 5, and a switching diode 15. The base bias voltage of the transistor 10 is given by resistance division between resistors 10 and 11, and an AGC control voltage is further applied from a terminal 20 via a resistor 12 and a switching diode 15. When the signal level input from terminal 1B is low, the AGC control voltage applied from terminal 20 is affected, and this AGC control voltage is higher than the voltage divided by the resistors 10 and 11. Next, a current flows through the switching diode 15, and a bias proportional to the AGC control voltage is applied to the base of the transistor 1.On the other hand, when the signal level input from the terminal 18 is low,
The AGC 11L voltage applied from the terminal 20 decreases, and when this AGC control voltage becomes lower than the voltage divided by the resistors 10 and 11, the switching diode 13 turns off and the transistor 10 base 2 resistance 1
A constant voltage resistance-divided by 0 and 11 is biased. By adopting the base bias circuit as described above.

Even when the A G CjelJ control voltage decreases, the collector current of the transistor 1 is maintained at a constant value, and the ffl characteristics do not deteriorate. Next, a bias is supplied from the power supply to the collector 4 of the transistor 1 through the resistor 8, and a bin diode 50 is lifed. The anode of this bin diode 5' is biased with a fixed voltage by the resistance division of resistors 6 and 7, and a high frequency signal is outputted from the anode of the bin diode 5 through a capacitor 16 and a terminal 19. In general, in a Bin diode, the island frequency resistance value is very large, and the bias region where it has a sufficient effect on high frequency signal attenuation is the bias region between the Bin diode's anode and cathode, which is the PNMN polymerization difference of the Bin diode ( 0.7 in silicon
V ) or below (a state in which the fully bin diode transitions from an ON state to an OFF state), and this transition region is also actively utilized in the present invention.

In other words, the input signal level input from terminal 18 increases, the AGC control voltage applied from terminal 2o decreases,
When the collector current flowing through transistor 1 decreases, the voltage drop across resistor 8 becomes smaller and transistor 1
, that is, the anode voltage of the pin diode 5 increases. At this time, if the anode voltage of the pin diode 5 rises higher than the fixed voltage biased to the cathode of the pin diode 5 by the resistors 6 and 7, the pin diode 5 becomes OFF state, and the pin diode 5
The high frequency resistance increases, and the signal level decreases. vice versa,
The input signal level input from terminal 1 falls, the AGC control voltage applied from terminal 20 rises, and the collector current flowing through transistor 1 increases.

The voltage drop caused by the resistor 8 becomes thicker, and the collector voltage of the transistor 1, that is, the anode voltage of the pin diode 5 decreases. When the anode voltage of the diode 5 falls, a minute current flows into the pin diode 5, the high frequency resistance of the pin diode 5 decreases, and the amount of signal attenuation becomes small. resistance 8
Due to the voltage drop caused by this, pin diode 5 is turned on.

This is a circuit that attenuates the signal level by turning it off.The amplifying transistor 1 also serves as the pin diode driving transistor, and a part of the collector current flowing through the transistor 1 is used to drive the pin diode 5. Therefore, the AGC circuit is small and has low power consumption. In the circuit of the present invention, a low capacitance capacitor 14 is connected between the bin diode 50 cand and the anode in order to keep the amount of signal attenuation below a certain value even if the AGC control voltage decreases. (Fig. 1 (α)) Also, instead of this low-f capacitor, as shown in Fig. 1 (bl), a circuit in which a large-capacity capacitor 26 and a resistor 22 are connected in series is connected to a pin diode 5. The circuit of the present invention may be connected between the anode and the cathode.
A case where it is used in a 1 fHz band second IF circuit will be explained. A satellite broadcast receiver consists of a BS converter and a BS tuner, and a signal converted from a 12 GHz band signal to an I GHz band 11F signal by the BS converter is input to the BS tuner. In the BS tuner, the received I
Select the desired signal from the 11th F signal of the GH1 band and tune to 4.
It is converted into a second IF signal of the 001 Xi 2 band and demodulated. Here, the input level of the BS chainer is -20 to -60 dBm.
Since there is a gap of 40 cLB, an AGC circuit is required to make this level the same. Z? , 5 tuners, in order to prevent deterioration of NFt% characteristics and distortion characteristics, a two-stage AGC in which AGC is applied in the 11th F circuit and the 21st F circuit is generally used. more than so dB,
2nd IF circuit's AGCC and below 2nd AGC circuit) is approximately 1o
dB gain control is performed, the second AGC circuit is operated at a high AGC control voltage, and the first AGC circuit is operated at a low AGC control voltage. For this reason, A.G.
Approximately 10 dB attenuation is obtained at a control voltage of 5 to 4 V, and the gain does not change below 4 V @ 2 A
A GC circuit was required. For this reason, in the AGC circuit of the present invention, bias conditions are set such that the AGC control voltage supplied from the lake child 20 is 5V and the pin diode 5 makes a DVC transition from ON to OFF, and further,
The AGC control voltage is attenuated by 10 dB around 4 V, and the pin diode 50 is connected to a capacitor 14 that does not attenuate any further.
The cathode and anode were connected. FIG. 2 shows the characteristics when the circuit of the present invention shown in FIG. 1 is used as a 400 AfHz band AGC circuit of a satellite broadcasting receiver. At an AGC control voltage of 5 to 4 V, good characteristics with a gain control width of about 12 dB are obtained.

FIG. 3 shows a second embodiment. This is a circuit that uses a choke coil 25 to supply bias from the power supply as a fixed bias for the anode of the pin diode 5.
The operation is similar to that of the embodiment shown in FIG. 1, and the same effects can be obtained.

FIG. 4 shows a third embodiment. This is a circuit in which a Zener diode 24 is used to supply a bias as a fixed bias to the anode of the pin diode 5, and operates in the same manner as the embodiment shown in FIG. 1, and provides similar effects.

Fig. 5 shows a fourth embodiment, in which resistors 25 and 27 are connected to a transistor 10 pace 2, and one is used as a power supply voltage supply terminal and the other as an AGC control Hoo supply terminal. Even if the AGC control voltage becomes a small value near OV, the transistor 10 base 2 is biased with the voltage determined by the power supply voltage and resistors 25 and 27, and current flows through the transistor 1, causing deterioration of the distortion characteristics. It's a shame. Even if this circuit is used, the same operation as the embodiment shown in FIG. 1 can be performed and the same effect can be obtained.

〔Effect of the invention〕

The present invention applies an AGC control voltage to the base of an amplifying transistor, and uses the voltage drop across the transistor's collector resistance to attenuate the signal level by turning on and off the bin diodes connected to the transistor's collector K. The amplification transistor is also used as a driving transistor for the pin diode, and a portion of the collector current flowing through the transistor is used to drive the pin diode, making it a small and low power consumption AGC circuit.
A circuit is obtained.

[Brief explanation of the drawing]

FIG. 1 (αl, (jl) is a circuit diagram of the first embodiment of the present invention, FIG. 2 is a characteristic diagram of the circuit of the present invention, and FIGS. It is an example circuit diagram. 1... Transistor 5... Pin diode 1
'5... Switching diode 20... AGC control voltage application terminal 21... iE power supply voltage application terminal 23... Choke coil 24... Zener diode Fig. 1 (cL) AeC Toka Iizo ( ■U

Claims (1)

[Claims] 1. In an AGC circuit consisting of a transistor and a pin diode, the cathode of a pin diode is connected to the collector of the transistor, a bias is supplied to the cathode via a resistor, and a fixed bias is supplied to the anode of the pin diode. An AGC circuit, further comprising means for applying an AGC voltage to the base of the transistor.