JPS5999877A - Agc system of receiving amplifier - Google Patents

Abstract

PURPOSE:To decrease the generation of noise when an input signal is small, by changing only the attenuation of an attenuation circuit of the front-stage or the rear-stage by means of an output of a detecting circuit detecting the level of an output signal to make the output level constant at all times even if the input level is fluctuated. CONSTITUTION:A TV radio wave received on an antenna 1 is amplified at a receiving amplifier 2 of broad band type, branched and amplified at a main line branching amplifier 8 via a branching device 12, applied to a TV receiver 14. An amplifier section 5 of the amplifier 2 consists of a preamplifier circuit 15, a pre-stage attenuating circuit 18, a middle stage amplifier circuit 16, a post- stage attenuation circuit 19, a post-stage amplifier circuit 17, a detecting circuit 20, a detecting circuit 21, a comparison circuit 22, and front-stage and rear-stage attenuation control circuis 23, 24 and the like. When the output level detected by the circuit 21 is a standard value or below, the attenuation of the circuit 19 is increased/decreased, the output level is made constant, and the attenuation of the circuit 18 is increased/decreased when the output level is a standard value or over, the output level is made constant, allowing to reduce the generation of noise when the input level is small.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AGC system for a receiving amplifier used in television communal reception, etc., and its purpose is to
Input material - In addition to the AGC operation that always sends out an output signal at a constant level even if the bow level fluctuates, the input level of the human input signal is low and the signal-to-noise ratio (carrier level and noise level of high-frequency signal A of the receiving amplifier that can amplify the noise generated inside the amplifier as much as possible even when the ratio (hereinafter referred to as the CN ratio) is small.
GC method: provided one by one.

The embodiments of the present application will be described below from the drawings.

Figure 1 shows joint television reception/steno reception using a reception amplifier.
In the system diagram Venus Sumono, ■ is the antenna that receives television waves. 2 is a wideband receiving amplifier, 3i-1:
The input terminal and 4 indicate the output terminal.As the receiving amplifier 2, a channel-dedicated type may also be used. Reference numeral 5 indicates an amplifying section, an l-input end, and 7 an output end. The configuration of the amplifier section 5 will be described in detail later. 08 is a main branch amplifier, 9 is an input terminal thereof, 10 is an output terminal, and 11 is a branch output terminal. 12 indicates a turnout. 13 is a transmission line, and a coaxial cable is used. 14 indicates a television receiver.

Next, FIG. 2 is a block diagram showing the configuration of the amplifying section shown in FIG. 1, and the same parts as in FIG. 1 are denoted by the same reference numerals. 15, 1.6, and 17 are in the previous stage, respectively.

This shows the middle-stage and rear-stage amplifier circuits, which amplify high-frequency signals such as television signals. 18 is a front-stage attenuation circuit provided between the front-stage amplifier circuit 15 and the middle-stage amplifier circuit J6;
Reference numeral 9 indicates a post-stage attenuation circuit provided between the middle-stage amplifier circuit 16 and the post-stage amplifier circuit 17, respectively.

20 is a detection circuit for detecting the output level of the amplified signal, and a well-known branch circuit or the like is used.

Reference numeral 21 denotes a detection circuit, which serves to convert a high frequency signal into direct current. 22 is a comparison circuit that uses the output of the detection circuit 21 to compare whether the output level of the high frequency signal is higher or lower than the standard, and outputs the result.

For example, it outputs a self-current voltage whose magnitude corresponds to the magnitude of the output level. 23 and 24 are respectively the front stage attenuation control circuit,
This is a post-stage attenuation control circuit. The pre-stage attenuation control circuit 23 controls all the damping characteristics of the pre-stage attenuation circuit 180.
Control is performed so that the result is as shown by the solid line in Figure (A). Note that the horizontal axis indicates an example of the output voltage at the output terminal P point of the comparator circuit 22. The second-stage attenuation control circuit 24 controls the attenuation characteristics of the second-stage attenuation circuit 19, for example, as shown by the solid line in FIG. 3(B). Note that the horizontal axis is an example of the output voltage at the output end point P. For comparison, the attenuation control circuit 23
．． Pre-stage attenuation circuit 18 without 24. Post-stage attenuation circuit 1
The attenuation characteristics of 9 are shown in Fig. 3 (A) and Fig. 3 (B), respectively.
is indicated by a broken line.

The operation of the amplifying section 5 having the second configuration will now be explained using the level diagram shown in FIG. 4 of C1. In FIG. 4, the horizontal axis shows the block circuits in positions corresponding to the respective block circuits in FIG. 2, with all the blocks in parentheses, and the vertical axis shows the level at that position. Note that this level diagram shows the state after the attenuation amount of the attenuation circuits 18 and 19 has settled down to a constant value.

First, when the input signal has a low level of about 50 dBμ, as shown by the broken line X in FIG. It is. (This corresponds to the case where the output voltage at point P in Figure 3 is 0) Next, the level of the input signal is 60
In the case of a standard level of about dBμ, as shown by the broken line Y, the amount of attenuation in the front-stage attenuation circuit ↑8 is almost zero, and the amount of attenuation in the rear-stage attenuation circuit 19 is about 1.0 dB, and the output level is the same as that of the previous stage. No different than the case. (This corresponds to the case where the output voltage at point P in FIG. 3 is Vo/2) Furthermore, when the level of the input signal is as high as about 70 dBμ, as shown by the broken line Z, the pre-stage attenuation circuit 18. Post-stage attenuation circuit 19
The amount of attenuation in both cases is approximately 10 dB, and the output l/bel remains unchanged in this case as well. (This is P in Figure 3.
(This corresponds to the case where the output voltage at point is Vo) As the input signal level increases from a state lower than the standard, the attenuation amount of the post-stage attenuation circuit J9 begins to increase first, and the state becomes higher than the standard. When this happens, the amount of attenuation in the second-stage attenuation circuit 19 is saturated and the amount of attenuation in the first-stage amplification circuit 18 begins to increase, so that the signal is always output from the output end 7 at a constant standard output regardless of the level of the human input signal. Sent out.

Next, the noise figure, which is a parameter indicating the noise fat generated inside the amplifier section 5, will be explained. Pre-stage amplifier circuit 15
．． Middle stage amplifier circuit 16. The respective power gains of the post-stage amplifier circuit 17 are assumed to be G+, G2, and G3, and the respective noise figures are assumed to be F+, F2, and F3.

Also, the front stage attenuation circuit 18. Assuming that the attenuation amounts in the post-stage attenuation circuit 19 are Ll and L2, respectively, the overall noise figure T1 in the amplifier section 5 is expressed by the following equation.

3-1 Ten ・ ・
・ ・ ・ ・(1) Gl−G2/ (Ll・L2) If we substitute the relational expression of the characteristics shown by the solid line in Fig. 3 for the attenuation amount Ll + L2 in equation (1), we get
The overall noise figure F will be found.

FIG. 5 is a chart showing an example of the overall noise figure characteristics of the amplifying section 5 with respect to the input signal. In the figure, the solid line indicates the embodiment of the present application, and the broken line indicates the attenuation control circuit 23.2.
4 shows the characteristics of the conventional one in which the number 4 is not provided. The device of this application can be used even if the input signal level is lower or higher than the standard.
Even if the standard is very low, it is possible to reduce the N index in general. This means that the C of the signal applied to the input terminal 6
This means that the signal can also be transmitted at the output terminal 7 without significantly deteriorating NJ+'J.

In the digital/video joint reception system shown in FIG. 1 using the reception amplifier 2 equipped with the amplification section 5 as described above, the signal strength of the television signal received by the antenna 1 is affected by seasonal changes, fading, etc. Even if the output terminal 1 of the reception amplifier 2 changes, the television signal can always be sent out at a constant standard level.

- Since the signal applied to the input terminal 3 of the receiving amplifier 2 can be sent from the output terminal 4 without significantly deteriorating the CN ratio,
In the FTV receiver 14 connected to the rear stage, it is possible to easily watch television with clear images with little snow noise.

Next, FIG. 6 is a circuit diagram showing a specific configuration of a part of the amplifying section 5. Components corresponding to those in FIG. 2 are designated by the same reference numerals as 2, and redundant explanation will be omitted. The attenuation circuits 18, 19+ are each constructed in the form of a bridge T-type.

25, 26.39.40 are PI as variable attenuation elements
N diodes, 27, 28, 41, and 42 respectively indicate resistances as constant resistance elements. 29.30.31, 32
．． 43.44° and 45.46 indicate resistors for biasing the PIN diode. 33.47 is choke coil,
34.35.36.37゜38, 48.49.50.5
] and 52 indicate capacitors that pass high frequencies and block direct current. Note that output signals (DC voltage) from the comparator circuit 22 are applied to terminals 18a and 19a, and terminals 7-18b and 52 are connected to terminals 18a and 19a, respectively. between 18c and terminal], 9b
A voltage for operating each PIN diode is applied between and 19c. The next VC pre-stage attenuation control circuit 2; 3 includes a Zener diode 53, a power supply (+B1),
It is composed of a resistor 54. The power supply (-1-Bl) supplies the voltage Vo explained in FIG. 3 to each circuit. The sonar diode 53 has a reference voltage of Vo/2.

The latter-stage attenuation control circuit 24 includes a Zener diode 55, a power supply (182), and a resistor 56. Power supply (+
The voltage of B2) and the reference voltage of diode 55 are the same as the voltage of power supply (10B1) and the reference voltage of diode 530, respectively.

In FIG. 6, even if the terminals 23c and 2.1b are all connected and one of the Zener diodes 53 and 55 is removed, the same control effect as in FIG. 6 can be obtained.

Next, Fig. 7 (Receiving amplifier % of liS'I + - ru configuration:
＞11 '-, J" Block circuit diagrams that are the same as those in Figure 1 or have equivalent functions are indicated by the letter e, iJ, e', e", etc. The redundant explanation will be omitted.The illustrated one shows a channel-dedicated type receiving amplifier, and 57, 57', . . .
57'' represents a bandpass filter dedicated to each television channel or FM station. 58 represents a mixing circuit.

As described above, the present invention can provide a receiving amplifier that always sends out an output signal amplified to a constant standard level even if the input signal level fluctuates.Moreover, the input signal level is low. Even when the CN ratio is small, the noise generated inside the amplifier is minimized and amplified, and the output signal is transmitted without deterioration as much as the CNN alloy.
It has the effect of being able to

[Brief explanation of the drawing]

The drawings relate to embodiments of the present invention, and Fig. 1 is a system diagram of TV joint reception/Sudem using a reception amplifier, Fig. 2 is a block diagram of the configuration of the amplifier section, and Fig. 3 (A>, C).
B> is a diagram showing the attenuation characteristics of the front-stage attenuation circuit and the rear-stage attenuation circuit, respectively. Figure 4 is the level diagram of the amplification section.
The figure shows an example of the characteristics of the overall noise figure of the amplification section that slopes to the input l/bell. Block circuit diagrams illustrating receiver amplifiers of different configurations. 3... Input terminal, 4... Output terminal A, 15... Pre-stage amplifier circuit, 16... Middle-stage amplifier circuit, 17... Post-stage amplifier circuit, 18... Pre-stage attenuation circuit, 19... - Post-stage damping circuit, 20... Detection circuit, 23... Pre-stage damping control circuit, 24... Post-stage reward reduction control circuit. Special applicant Maspro “IL Engineering Co., Ltd. Representative
Takashi Hayama Figure 5 4 (

Claims (1)

[Claims] A front-stage amplifier circuit, a front-stage attenuation circuit, a middle-stage amplifier circuit, a rear-stage attenuation circuit, and a rear-stage amplifier circuit are interposed in cascade between the input terminal and the output terminal f-, and between the rear-stage amplifier circuit and the output terminal. A detection circuit is provided to detect the output signal level.
Moreover, the first-stage reduction circuit controls the attenuation amount with the first-stage attenuation side φ1j circuit, and the second-stage attenuation control circuit (7#, 111) controls the attenuation amount by the first-stage attenuation side φ1j circuit. In the amplifier, when the level of the output signal detected by the above detection circuit changes from a state lower than the standard to the standard state, the attenuation amount of the above-mentioned front-stage attenuation circuit is not changed. When the level of the output signal in the detection circuit is from the standard state to a state higher than the standard, the attenuation amount of the latter stage attenuation circuit is increased or decreased so that the output level becomes constant. An AGC method for a receiving amplifier characterized in that the output level is made constant by fully increasing or decreasing the amount of attenuation of the pre-stage attenuation circuit L without changing the @.