JPH0448059Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field This invention relates to an audio signal amplification circuit for a television receiver, and more specifically to an audio signal amplification circuit that amplifies FM audio signals and AM audio signals.

(b) Conventional technology In Europe, including Japan, TV audio signals are transmitted as FM signals. However, in France, even in Europe, audio signals are
It is transmitting as an AM signal. Therefore, there are generally different trends in Europe and France.
In order to be able to receive both TV audio signal transmission methods, as shown in Figure 2, block A is required.
An amplifier circuit and a detector for the FM audio signal as well as an amplifier circuit and a detector for the AM audio signal shown in block B are provided independently.
A switch 20 is used to switch between the AM audio signal and the AM audio signal.

In other words, the tuner 21, the PiF amplifier circuit 22 and PiF detector 23 in block C, and the SiF circuit shown in block A are the same circuits as in general TVs with specifications for the European region, and the AM Added audio signal processing circuit.
By providing two amplification circuits, an FM audio amplification circuit and an AM audio amplification circuit, the FM audio signal and
It is designed to be able to receive both AM audio signals.

(c) Problems that the invention aims to solve However, in the above audio amplification circuit, filters and amplifiers that have the same functions for both circuits are used redundantly in the FM audio amplification circuit and the AM audio amplification circuit. This not only increases manufacturing costs but also reduces work efficiency due to the large number of parts.Additionally, having an extra circuit in a tuner that requires faithful signal transmission is unnecessary. There was a problem that noise components were generated.

This idea was made in view of the above circumstances,
One of the purposes is to greatly simplify the audio circuit by sharing the FM audio signal amplification circuit and the AM audio signal amplification circuit, and the other purpose is to improve work efficiency and reduce costs. There is a particular thing.

(d) Means for solving the problem This invention includes a tuner, a video signal intermediate frequency amplification circuit that amplifies the video intermediate frequency signal from the tuner, and a video signal intermediate frequency amplification circuit that amplifies the audio intermediate frequency signal from the video signal intermediate frequency amplification circuit. In a TV receiver equipped with an audio signal intermediate frequency amplification circuit, the audio signal intermediate frequency amplification circuit includes an audio intermediate frequency amplification means for amplifying the FM audio signal and the AM audio signal at different amplification factors, and the audio intermediate frequency amplification circuit. FM detector and AM connected to the output of the vehicle
If the audio signal received by the detector and the tuner connected to both detectors is an FM audio signal, the FM detector and the audio signal received are
In the case of an AM audio signal, there is a first switching means that operates each of the AM detectors, an amplitude detection means that is connected to the output of the AM detector and keeps the output amplitude of the AM audio signal constant, and a first switching means that operates each of the AM detectors. is a constant voltage means for operating the audio signal intermediate frequency amplification means at a predetermined amplification factor, and the first switching means.
While the detector is in operation, the output signal and the output voltage from the constant voltage means are switched so that the audio signal intermediate frequency amplifying means is operated at a predetermined amplification factor by the output signal from the amplitude detecting means. This TV receiver is characterized by comprising second switching means for inputting to the amplification means.

(e) Effect This device is designed so that when the first switching means switches to the FM detector side, the second switching means also connects the audio intermediate frequency amplification means and the constant voltage means, and the maximum gain is achieved by the audio intermediate frequency amplification means. The amplified FM audio signal is output through an FM detector. Further, the first switching means
When switching to the AM detector side, the second switching means is also linked,
This time, the audio intermediate frequency amplifying means and the amplitude detecting means are connected, and the audio intermediate frequency amplifying means operates to keep the output amplitude constant and output the amplified AM audio signal through the AM detector.

(F) Example This invention will be described in detail below based on the example shown in FIG. Note that this invention is not limited thereby.

FIG. 1 is a block diagram of the audio signal amplification circuit and video signal amplification circuit 2 when receiving an FM audio signal of this invention. In the figure, the audio intermediate frequency signal ( As an example, 6.5MHz) is used as an audio intermediate frequency signal (6.5MHz) by SiF (sound intermediate frequency) filter 4.
The audio intermediate frequency amplifying means 5
primary, secondary, and tertiary amplifiers 6, 7,
8. Audio intermediate frequency is an example of
Although 6.5MHz was used, the frequency set differs depending on the transmission method of each country, so when the audio intermediate frequency signal is 5.5MHz or 6.0MHz, a frequency converter (not shown) is usually added to the front stage of the SiF filter 4.
Configure to use any of 5.5/6.0/6.5MHz.

The primary, secondary, and tertiary SiF amplifiers 6, 7, and 8 are amplifiers that can obtain a high gain by adjusting the gain, and the audio signal output from the tertiary SiF amplifier 8 is connected in parallel to the output side of the tertiary SiF amplifier 8. The selection signal is supplied to the FM detector 9 and AM detector 10 connected by Therefore, the signal is switched to be input to one of the detectors 9 and 10. This embodiment shows a state in which the FM detector 9 is operating. FM detector 9 and
The output side of the AM detector 10 is connected, and the FM audio signal selected by the switch 11 or
One of the AM audio signals is output. In addition, the output side of the AM detector 10 is SiF/AGC
It is fed back to the detector 12. This SiF/AGC detector 12 detects the amplitude of the audio signal output from the AM detector 10 and controls the gains of the primary, secondary, and tertiary SiF amplifiers 6, 7, and 8, so that the amplitude of the audio signal is The amplitude detecting circuit 13, which will be described later, operates to maintain a constant amplitude.

As is known, the FM wave has a constant amplitude as shown in Fig. 3, and the audio signal is modulated and transmitted by changing the frequency, so the primary, secondary, and tertiary amplifiers 6, 7, and 8 operate at high gain. It is sufficient to perform an amplitude control operation. Since it is known that amplitude control is performed by the saturation operation of the amplifier, the linearity of the amplifier can be ignored in the amplification of FM waves. On the other hand, as shown in Figure 4, in the case of AM waves, the audio signal is transmitted as amplitude changes, so the primary, secondary, and tertiary SiF amplifiers 6, 7, and 8 operate within a range with good linearity without becoming saturated. Therefore, an amplitude detection circuit 13 is essential to keep the output amplitude constant.

This invention focuses on the characteristics of the above FM waves and AM waves,
When receiving FM audio signals (general Europe area),
A switch 14 provided in the amplitude detection circuit 13 switches the primary, secondary, and tertiary SiF amplifiers 6, 7, and 8 to a fixed voltage 15 as a constant voltage means that operates at maximum gain, and receives AM audio signals (France area). When the switch 14 as the second switching means is
By switching to the AGC detector 12 side, the primary
2nd and 3rd order SiF amplifiers 6, 7, 8 with AM and FM
It is designed so that it can be shared by both transmission systems. Note that the switch 14 and the switch 11 are provided so as to operate in conjunction with each other, and
The selection signal is supplied from the operating section or the system discrimination circuit.

(G) Effects of the invention According to this invention, it is possible to greatly simplify the amplification circuit that amplifies the FM audio signal and the AM audio signal. It is possible to reduce the cost of the signal amplification circuit.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the FM/AM audio signal amplification circuit of this invention, Figure 2 is a diagram corresponding to Figure 1 of the conventional example, Figure 3 is an explanatory diagram showing FM waves, and Figure 4 is
FIG. 3 is an explanatory diagram showing AM waves. 1...Audio signal intermediate frequency amplification circuit, 5...Audio intermediate frequency amplification means, 9...FM detector, 10...
AM detector, 11...first switching means, 13...amplitude detection circuit, 15...constant voltage means, 14...second
switching means.

Claims (1)

[Claims for Utility Model Registration] A tuner, a video signal intermediate frequency amplification circuit that amplifies the video intermediate frequency signal from the tuner, and an audio signal intermediate frequency amplification circuit that amplifies the audio intermediate frequency signal from the video signal intermediate frequency amplification circuit. TV with
In the image receiving device, the audio signal intermediate frequency amplification circuit includes audio intermediate frequency amplification means for amplifying the FM audio signal and the AM audio signal at different amplification factors, and an FM detector connected to the output of the audio intermediate frequency amplification means. and A.M.
If the audio signal received by the detector and the tuner connected to both detectors is an FM audio signal, the FM detector and the audio signal received are
In the case of an AM audio signal, there is a first switching means that operates each of the AM detectors, an amplitude detection means that is connected to the output of the AM detector and keeps the output amplitude of the AM audio signal constant, and a first switching means that operates each of the AM detectors. is a constant voltage means for operating the audio signal intermediate frequency amplification means at a predetermined amplification factor, and the first switching means.
While the detector is in operation, the output signal and the output voltage from the constant voltage means are switched so that the audio signal intermediate frequency amplifying means is operated at a predetermined amplification factor by the output signal from the amplitude detecting means. 1. A TV receiver comprising: second switching means for inputting to the amplification means.