JPH04192891A - Reception circuit - Google Patents

Abstract

PURPOSE:To reduce the power consumption and to integrate a circuit by providing an AGC circuit on a reception circuit, which detects the input level of an antenna with a detection circuit, generates a control signal and controls the gain of an RF amplifier having a variable gain function. CONSTITUTION:An AGC loop consists of an RF amplifier 11, a mixer circuit 12, a band pass filter 18 and a detection circuit 19. Thus, a signal exceeding a prescribed signal level is not inputted to an IF amplifier 14 at the output terminal of the AGC loop through the AGC operation and the output dynamic rage of the IF amplifier 14 is not requested unnecessarily. Thus, the circuit with an excellent distortion characteristic even at a low voltage is realized and the circuit suitable for circuit integration is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a receiving circuit used in, for example, a television receiver or the like.

(Prior art) The audio tuner circuit of a conventional television receiver is
It has a block configuration as shown in FIG. That is, 10 is an antenna section of a tuner input terminal, and a signal inputted from this antenna section 10 is manually amplified by an RF amplifier 11 whose gain can be varied. The output of the RF amplifier 11 is input to one side of a mixer circuit 12, and the other side of this mixer circuit 12 is connected to a local oscillator 13.
The mixer circuit 12 outputs an intermediate frequency signal. The output of the mixer circuit 12 is supplied to an IF amplifier 14, where it is amplified. The output of this IF amplifier 14 is supplied to a SAW filter 15, which is a bandpass filter that creates a Nyquist slope, and the output of the SAW filter 15 is supplied to a demodulation circuit 16, where it is demodulated and becomes a video output and an audio output. . In this demodulation circuit 16,
The demodulated signal amplitude level is detected, and when an input above a certain window is input to the demodulation circuit 16, it is fed back to the RF amplifier 11 as an AGC signal 17 and multiplied by 800.

In a tuner circuit having such a configuration, the antenna input level generally has a wide input level range of 30 dBμ to 120 dBμ. By the way, the SAW filter 15 also has a large amount of signal attenuation due to its SAW characteristics, generally -20d.
There are around B. The IF amplifier 14 connected to the SAW filter 15 requires a large gain to amplify the attenuation of the SAW filter 15. Further, the RF amplifier 11 and the mixer circuit 12 are designed to obtain a large gain in response to a small input signal from the antenna section 10.

In such a configuration, when a large input signal is input from the antenna section 10, the AGC signal 17 generated from the demodulation circuit 16 lowers the gain of the RF amplifier 11, thereby reducing the gain of the mixer circuits 12 and 14. This prevents the input level from becoming too large and resulting in poor performance.

However, in order to generate the AGC signal 17, the RF amplifier 11. mixer circuit 12 and IF amplifier 14,
An input signal that exceeds the signal level that is stabilized once these controls are applied is input.

At this time, the IF amplifier 14 functions as a tuner circuit.
Since it is the last amplification stage, it is necessary to output a signal with a fairly large amplitude.

Furthermore, these IF amplifiers 14 and mixer circuits 12 ensure a sufficient output dynamic range for input amplitudes greater than necessary in order to improve distortion characteristics, which are the fundamental characteristics that determine the performance of tuner circuits. This is required of the circuit.

In this way, in order to achieve a sufficient dynamic range and low distortion, the power supply voltage cannot be lowered, resulting in problems such as the inability to realize low power consumption and the inability to use ICs.

(Problem 8 to be Solved by the Invention) In conventional receiving circuits, it has not been possible to achieve a low power supply voltage while achieving sufficient dynamic range and low distortion for each circuit to accommodate large-amplitude inputs.

Therefore, it is an object of the present invention to realize a receiving circuit that satisfies the characteristics of the circuit, has low power consumption, and is suitable for IC implementation.

[Configuration of the Invention (Means for Solving the Problems) The receiving circuit of the present invention connects a detection circuit equipped with a bandpass filter between the output of a mixer circuit and the input of an IF amplifier, and uses this detection circuit to It is equipped with an AGC circuit that detects the input level of the antenna, generates a control signal, and controls the gain of an RF amplifier with a variable gain function.

(Function) In the receiving circuit of the present invention, the input of the IF amplifier, which is the output end of the AGC loop, is prevented from receiving an input with a signal level higher than a certain amount due to the operation of the AGC. Therefore, since the output dynamic range of the IF amplifier is not required to be greater than necessary, the receiving circuit can be designed with a low voltage and is suitable for IC implementation.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. The same parts as in FIG. 2 are given the same reference numerals.

In Figure 1, at the antenna part of the tuner input terminal,
The input high frequency signal is input to an RF amplifier 11 whose gain can be varied and amplified. The output of the RF amplifier 11 is input to one side of the mixer circuit 12, the output of the local oscillator 13 is input to the other side of the mixer circuit 12, and the mixer circuit 12 outputs an intermediate frequency signal.

The output of the mixer circuit 12 is supplied to an IF amplifier 14, where it is amplified. The other output is bandpass filter 1
8 is connected. The output of the bandpass filter 18 is supplied to the detection circuit 19, and the output of the detection circuit 19 is supplied to the AGC.
Feedback to IF amplifier 11 as signal 17'
GC is applied. The output of the 1F amplifier 14 is supplied to a SAW filter 15 which serves as a bandpass filter. S
The output of the AW filter 15 is supplied to a demodulation circuit 16, where it is demodulated and becomes a video output and an audio output.

In the tuner circuit having such a configuration, when a high level input is input to the antenna section 10, the AGC
The signal 17' is generated by a detection circuit 19 through a band pass filter 18 which selects only the frequencies in a necessary band from the signal level output from the mixer circuit 12.

As a result, the AGC signal 17- having the input signal level of only the selected channel is obtained. This AGC signal 17'
is set to occur when an input signal above a certain level is input. As a result, the RF amplifier 11 is set to attenuate its gain. From the above operation, R
The F amplifier 11, mixer circuit 12, bandpass filter 18, and detection circuit 19 constitute an AGC loop.

Therefore, in a tuner circuit with such a configuration, the AGC
At the input of the IF amplifier 14, which is the output end of the loop, A
Due to the operation of the GC, inputs with a signal level above a certain level are not input. Therefore, the output dynamic range of the IF amplifier 14 is not required to be greater than necessary.

[Effects of the invention] In the tuner circuit configured as described above, the output dynamic range of the IF amplifier in the final output section is good up to the level at which AGC is applied to the RF amplifier, so there is no need to drive large amplitudes, and even low voltage can be achieved. Since a circuit with good distortion characteristics can be realized, a circuit suitable for IC implementation can be realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a tuner circuit according to the present invention, and FIG. 2 is a block diagram of a conventional tuner circuit. 11... RF amplifier 12... Mixer 14... IF amplifier 16... Demodulation circuit 18... ...Band pass filter 19...
...Detection circuit 17'...AGC signal

Claims (1)

[Claims] A variable gain amplifier circuit that amplifies a high frequency signal input from an antenna, a frequency converter that converts the output of the amplifier circuit and the oscillation frequency of a local oscillator to obtain a predetermined intermediate frequency, and an output signal of the frequency converter. a first detection circuit that detects the output of the amplification circuit; a bandpass filter that passes the output signal of the frequency conversion means; and a second detection circuit that detects the output of the bandpass filter. A receiving circuit comprising: a detection circuit; and means for controlling the gain of the variable gain amplifier circuit using the output of the detection circuit.