FI63508B - KOPPLING VID EN TELEVISIONSMOTTAGARE FOER DETEKTERING AV LJUDSIGNALER SOM SAENTS ENLIGT OLIKA SAENDNINGSNORMER - Google Patents

Description

1 63508

Connecting a television to detect audio signals transmitted according to different transmission standards

The present invention relates to a coupling of a television set for separating and detecting audio signals transmitted according to different transmission standards, which coupling includes an intermediate frequency filter, an associated audio channel intermediate frequency detector having an output signal frequency.

In a television broadcast, the difference between the audio and video carrier frequencies depends on the TV broadcast standard. Frequency modulated audio is transmitted according to different standards with a different frequency difference from the image carrier frequency. The following frequencies are used: 4.5; 5.5; about 5.75; 6.0 and 6.5 MHz (approx. 5.75 will be used with the TV stereo).

If it is desired to receive transmissions in accordance with different standards on the same TV set, the intermediate frequency part of the TV must be constructed in certain respects in such a way that the circuit parts affecting the standard can be replaced by suitable switching elements. Known methods are: 1. Switching filter parts and detector parts with switches.

2. Use the switches to replace the filter parts and the tuned part of the detector (synchronous detector tank circuit).

3. Switch the filter parts with the switches and mix the appropriate frequency from one or more external sine oscillators via the switches, whereby the separation frequency corresponds to the tuning of the detector part.

The disadvantages of the above solutions are the following when making a multi-norm detector: 2 63508 a) switching stages are needed in two places b) circuit solutions are complex c) tuning measures are required d) switching is difficult to add to the receiver afterwards e) there are several different module variations when using e.g. one additional standard.

For example, DE 29 29 565 discloses a circuit for receiving television audio signals according to different standards, which circuit comprises a selective front circuit for different frequencies, a mixer and an oscillator, the frequency of which depends on the received standard and is automatically selected by a discriminator. However, this known connection has the disadvantages listed above a) ... d).

The object of the present invention is to eliminate the above-mentioned disadvantages and, in particular, to provide a connection in which the number of switches required is even smaller and which is also easy to connect to the receiver afterwards.

To achieve this object, the invention is characterized in that a standard module is connected between the audio intermediate frequency detector and the audio detector, comprising a harmonic oscillator, the frequencies of which are multiples of the selected base and the highest frequency lower than the frequency to be detected, switches on and off the frequency ranges correspond to different transmission standards, as well as a mixer, said components of the module being connected such that the signal passes through the filter part and the mixer through the module, mixing with the signal from the harmonic oscillator in the mixer.

3,6508 Thus, a harmonic oscillator is an oscillator whose output voltage frequency spectrum includes, in addition to the fundamental frequency f1, its multiples 2f ^, 3f ^ ... nf ^, however, so that the maximum frequency nf ^ is less than the frequency f ^ to be detected. For example, when the fundamental frequency of the oscillator is = 250 kHz, the basic frequency and the frequencies 2f ^ and 4f ^ also make it possible for the known sound carrier transmissions 4.5 MHz, n.

5.75 MHz, 6.0 MHz detection with 5.5 MHz basic detector.

The output side of the module preferably has a bandpass filter after the mixer before the sound detector.

The connection also preferably has a module bypass, which is provided with a switch, which switch is closed when the reception takes place in the so-called according to the basic standard.

The invention and its other features will be described in more detail below by way of example and with reference to the accompanying drawings, in which Fig. 1 shows in block diagram form a television receiver connection according to the invention, separating image and audio signals and detecting audio signals, 4 63508 Fig. 2 shows an essential part of a connection and Figure 3 shows a component-specific implementation of the module.

In Fig. 1, reference numeral 1 denotes an intermediate frequency filter, the input signal of which is formed by the difference frequency of the frequency of the received signal and the local oscillator. The intermediate frequency filter distinguishes between the audio carrier frequency and the video carrier frequency of the new f ^ ·

Since the present invention is specifically directed to the processing of an audio signal, the part of the receiver after the image detector 3 is not shown. Thus, in the known connections, the parts of the intermediate frequency filter 1 as well as the audio frequency frequency detector 2 have to be varied in order to receive the signals transmitted according to different norms as described above.

However, according to the present invention, a standard module 5 is connected between the intermediate frequency detector 2 and the sound detector 4, which makes the replacement of other parts unnecessary and the connection and purpose of which are described in more detail below.

The block diagram structure of the standard module 5 is shown in Figure 2. It consists of a logic part comprising parts 6-9 and an oscillator stage comprising parts 10, 11. On the input side of the signal, there are first a number of parallel bandpass filters 6, the frequency ranges F1 .., F1 corresponding to frequencies according to different transmission standards and which can be turned on by switches 7. These switches are in turn controlled by a logic circuit 8 by manual or automatic selection. the norm of the signal just received. If this is the basic norm for which the intermediate frequency stage 1.2 has already been dimensioned, the logic circuit 9 controls the switch Sg so that the signal 5 63508 passes directly through to the bandpass filter 12.

An important part of the module is the harmonic oscillator 10, which at the same time generates harmonic "auxiliary frequencies". By mixing the frequencies of the oscillator with the output frequency of the respective filter 6, a signal according to the norm is obtained for the sound detector 4 via the band-pass filter 12.

An example of a component-specific solution of a standard module is shown in Figure 3. It has a control and logic part implemented with fixed logic, but of course it can also be easily implemented with a microprocessor. The signal FM of the image is applied to the filter section with the filters Sj, Sjj corresponding to each desired norm in parallel. Then, a signal is applied to the mixer (T2) via the switch part (D1, D2, D3), to which the signal of the harmonic oscillator is also input, whereby the mixing result is the frequency FMQUt (for the detector stage) of the norm corresponding to the sound detector.

The logic part encodes certain norms for certain channel numbers from the channel number information (BCD code) (correspondingly, the microprocessor application allows arbitrary channel numbers).

By disconnecting the control (e.g. resistors R4 or R ^), the bypass switch Sg operates, where FM ^ n = FMQut. The harmonic oscillator is crystal controlled, so it does not require tuning. The fundamental frequency of the oscillator is selected so that the frequency raster outputs frequencies of 500 kHz and 1 MHz. Similarly, it can provide a frequency raster at 250 kHz intervals if it is desired to detect a transmission of about 5.75 MHz. The frequency raster is made to suit the FMqu ^ frequency.

6 63508

The disclosed circuit according to the invention thus comprises one switching stage. There is only one harmonic oscillator in the circuit that does not need tuning. Therefore, the solution is simpler than previously used.

One circuit, which can be easily added to the TV afterwards, covers all the necessary FM standards.

Claims (4)

63508 7 A coupling of a television receiver for separating and detecting audio signals transmitted according to different transmission standards, the coupling comprising an intermediate frequency filter (1), an associated audio channel intermediate frequency detector (2) having an output signal frequency of a frame carrier frequency (fkk) and a sound carrier frequency (fkk) and a sound detector (4) connected after the intermediate frequency detector, characterized in that a standard module (5) is connected between the sound intermediate frequency detector (2) and the sound detector (4), which includes a harmonic oscillator (10) with frequencies selected - multiples of the cross-sectional frequency (f ^) and the highest frequency lower than the detectable frequency (fQ), filters (6) that can be switched on and off by switches (7), whose frequency ranges (Fa ... Fn) correspond to different transmission standards, and a mixer (11), and wherein said components of the module (5) are connected such that the signal passes through the filter part (6) and the mixer (11) through the module, mixing in the mixer harmon with the signal from the oscillator circuit (10). Connection according to Claim 1, characterized in that there is a band-pass filter (12) on the outlet side of the module (5) after the mixer. Connection according to Claim 1 or 2, characterized in that it also has a module bypass which is provided with a switch (Sg). Coupling according to one of the preceding claims, characterized in that said switches (7, Sg) are controlled electronic switches.