HU206173B - Sound carrier frequency filter system for a multi-standard television receiver - Google Patents

Abstract

The audio IF filter circuit described is suitable for use in a television receiver for decoding audio signals transmitted in any of a number of frequency standards. The circuit includes a tuner (1), first and second audio saw filters (2,3), a third audio saw filter (4), a video saw filter (5), and an audio IF demodulator (6). The tuner (1) supplies signals in parallel to the saw filters (2 to 5) and one of the audio filters is activated by control signals (Va to Vc) so as to give a desired filtering frequency depending on the frequency standard in use. The output signal of the activated one of the saw filters is supplied to the demodulator (6). The third audio saw filter is specially adapted so as to have first and second inputs (4a, 4b) which are connected to the tuner (1) by selection circuitry (Q1, D1, D2, L2, R1 to R3) for selecting one or other of the inputs (4a or 4b) in response to one of the control signals (Va). This allows the third audio saw filter to perform the function of two conventional such filters, thereby reducing the manufacturing cost of the filter circuit. <IMAGE>

Description

Description: 6 pages (including 2 pages)

HU 206 173 Β

The subject of the application is a speaker-frequency filtering system with parallel filters connected to the output of a tuner unit for multi-standard television receivers, corresponding to the speakers of different standards, the output of which is connected to switch transistors controlled by switching transistors.

The subject of the application is the so-called "loudspeaker frequency filtering system". It is used in parallel audio television receivers in which the video bandpass filter and the speaker frequency filtering system are connected in parallel to the tuner output.

Many television standards are known, such as: BG / H, M, L, L '. D / K, I norms. Different standards require different audio-picture frequency ranges, e.g.

4.5 MHz, 5.5 MHz, 6 MHz or 6.5 MHz.

These frequencies correspond to signals in the video center frequency range at the output of the tuner, e.g. 33.4 MHz for BG / H, 34.4 MHz for M, 32.4 MHz for L, D / K or I, 40.9 MHz for L '.

In the known embodiment of the audio filter system, which will be described in more detail below with reference to Figures (3) and (4), the output of the tuner unit is connected to each other and parallel to the video mid frequency band filters according to different standards. The output of the bandpass filters is connected to a voice carrier IF demodulator via switching transistors controlled by switching transistors, where a control signal is used to switch each bandpass filter.

The disadvantage of the known solution is that too many (five) bandwidths are loaded on the tuner output, so that its matching, correct matching of the bandwidth input impedance cannot be satisfactorily solved and since the bandwidths of the filters are asymmetric, failure, e.g. the filtering characteristic becomes asymmetric, which reduces the selectivity of the filtration by about 6 dB. In addition, the large number of components used is disadvantageous in terms of production cost.

It is an object of the present invention to overcome the above shortcomings. Accordingly, the present invention provides a bandpass filter connected to the output of a tuner-frequency filter system to a multi-standard television receiver tuned to parallel tuners of different standards, the output of the band filters being connected to a loudspeaker IF demodulator via switching diodes. is implemented as a bandpass filter which inputs are connected via an alternate switching circuit to the tuner unit output.

The alternative switching circuit is preferably implemented with a pair of diodes connected in parallel to the inputs of the dual band filter, wherein the anode of the diodes is connected to a power source through a choke coil and to a common input point of the dual band filter. The cathode of the first switching diode is connected via a capacitor to one output point of the tuner, the cathode of the second switching diode is connected to the other output point of the tuner, and the collector of the emitter switching transistor grounded via a resistor in the first switching diode. .

Preferably, one connection diode is connected between the output terminals of the bandpass filters and connected in series with one another. The beginning and the end of the diode array are connected to the IF demodulator input and a third control input is connected to the anode of the third switch diode forming the beginning of the diode array, the second control input is connected to the anode is connected to a collector of a grounded emitter switching transistor, which is connected to the second control input via a base anode of the switching transistor through a diode connected to the base circuit, and through a third diode connected to its anode through a further diode connected to the base circuit.

The advantage of the speaker frequency filtering system according to the invention compared to the known solutions is that the output of the tuning unit is less loaded with bandwidth filters, thus the fitting is better, the frequency characteristics of the band filters are not distorted due to fitting errors and the filtering system is simpler.

The following is a detailed description of the subject matter of the invention and a comparison with the prior art. In the drawing it is

Figure 1 is a schematic diagram of a filter system according to the invention, a

Figure 2 is a control algorithm for the filter system of Figure 1, a

Figure 3 is a schematic diagram of a prior art filter system, a

Figure 4 is a control algorithm for the filter system of Figure 3.

Figure 1 is a schematic diagram of a filter system according to the invention. (1) Inductively Separated (IFI, IF2) Outputs (Cl, C2) of Tuner Unit (L1) Separated by Capacitors Video-Medium Frequency (5) Band Filter, Tuned to 34.4 MHz (2) Band Filter, Tuned to 33.4 MHz ( 3) a bandpass filter and a dual-band, single-output dual band (4) tuned to 40.9 MHz and 32.4 MHz are connected, wherein the dual band (4) band filters (4a, 4b) are connected via an alternate switching circuit (4a, 4b). 1) connected to the tuner output.

The alternative switching circuit is implemented by means of connection diodes (D1, D2) connected in parallel with the inputs (4a, 4b) of the dual band filter (4), wherein the anode of the connection diodes (D1, D2) is connected to the power supply source (4) lane2

GB 206 173 Β is connected to the common input point of the filter. The cathode of the first switching diode (D1) is connected via a capacitor (C1) to an output point (IFI) of the tuning unit (1), and the cathode of the second switching diode (D2) is connected to the other output (IF2) of the tuning unit . In addition, the collector (R1) of a grounded emitter (Q1) is connected to the cathode of the first switching diode (D1) via a resistor (R3) connected to the base circuit of the switching transistor (Q1) to the cathode of the second switching diode (D2). The control input (Va) is connected via a resistor (R2) to the base of the switching transistor (Q1).

One of the output diodes (D3, D4, D5) is connected between the output terminals of the band filters (2, 3 and 4) and connected in series. The beginning and end of the diode array (C3 and C4) are connected via a capacitor to the center-frequency IF demodulator input (6). Further, a third control input (Ve) is connected to the third anode (D3) which forms the beginning of the diode array through a resistor (R9), while the cathode of the connecting diode (D3) and the fourth (D4) connecting cathode (R8) are grounded. A second control input (Vb) is connected to the anode of the fourth (D4) and to the cathode (R7) of the fifth (D5). The collector of the fifth transducer (D5) is connected to a grounded emitter (Q2) by a resistor (R6) which is connected to a ground of an emitter (Q2) by a base anode of a switch transistor (Q2) and a second (Vb) and connected via a further diode (D8) connected to a third control input (Ve). The base circuit of the switching transistor (Q2) consists of a diode (D6) connected to the base by a cathode and a resistor (R4) connected between the anode of the diode (D6) and the power supply (Vs), where the diodes (D7, D8) D6) are connected to the anode of the diode. The collector (R5) of the switching transistor (Q2) is connected via a resistor to the power supply (Vs).

The circuit arrangement according to the invention differs significantly from the known arrangement shown in Fig. 3, in which the audio carrier frequency (32,33, 34, 35) band filters and the video mid frequency band filter (36) simultaneously load the output of the tuning unit (31). The output of the band-pass filters (32, 33, 34 and 35) is asymmetric, with one of the terminals grounded and the other connected via a transistor-controlled switching diode to a common wire. This arrangement has a control input for each bar filter. The asymmetric load of the output of the bandpass filters due to the nonlinearity of the transistor and the scattered parameters distorts the filter characteristics, the simultaneous loading of the tuner unit with too many (five) bandpass filters spoils the filter matching of the known solution. The known arrangement requires control according to Fig. 4 depending on the norm (four control signals).

The speaker frequency filter system according to the present invention is illustrated by the example of FIG. The operation of the embodiment of the present invention is illustrated by the table in Figure 2:

The signals of the control inputs (Va, Vb, Ve) are used to select between the band filters (2, 3, 4) 5.

When receiving a BG / H standard TV broadcast, the signal displayed on the control inputs (Va, Vb, Ve) is "1", "0", "1" respectively, which causes the switching diodes (D1, D3) and diode (D7) conductors, the diodes (D2, D4) kap10 and the diode (D8) are off (open) so that the switching transistor (Q2) is closed, it is not conductive. Since the switching diodes (D3, D5) are short-circuited and the switching diodes (D4) are open, in this control state the output of the bandpass filter (3) is connected to the IF demodulator (6), the filter system 33,4 It transmits a mid-frequency center frequency signal.

When receiving a TV broadcast complying with standard M, the control inputs (Va, Vb, Ve) are in the order "1", "1", "0". Then, the switching diodes (D1, D4, D5) and the diode (D8) are switched on (conducting), the switching diodes (D2, D3) and the diode (D7) are switched off (open). In this control state, the output of the bandpass filter (2) is coupled to the IF demodulator (6), and the filter system transmits a 34.4 MHz audio mid-frequency signal corresponding to the M norm.

When receiving a L-compliant TV broadcast, the control inputs (Va, Vb, Ve) are in the order "1", "1", "1". In this case, the switching diodes (D1, D3, D4) are on (conducting), the switching diode (D2) is off (open) and the diodes (D7, D8) are off, so the switching transistor (Q2) goes to saturation, is on, so the switching diode (D5) is also off (open). In this control state, the output signal from the signal at the input (4b) of the bandpass filter (4) is output from the output of the bandpass filter (4) to the IF demodulator (6), which is a 32.4 MHz center frequency signal.

When receiving a TV broadcast conforming to the standard L ', the signals of the control inputs (Va, Vb, Ve) are "0", "1", "1" respectively. At this point, the switching diodes (D2, D3, D4) are on (conducting) and the switching diodes (D1, D5) are off (open). In this control state, the signal from the input (4a) of the bandpass filter (4) is output from the output of the bandpass filter (4) to the IF demodulator (6), which is a 40.9 MHz center frequency signal corresponding to standard (L ').

When receiving a TV broadcast according to D / K and I standards, the control state is the same as that of L standard, as the center mid frequency is 32.4 MHz.

Claims (3)

PATENT CLAIMS 1. A loudspeaker frequency filtering system having band filters corresponding to different standards of loudspeakers which are connected in parallel to the output of a tuner unit for a multi-standard television receiver, which: The output of the 60 band filters is controlled by switching transistors Connected to audio IF demodulator via switching diodes, characterized in that two different band filters are implemented as a single, dual-input dual band filter (4), which inputs (4a, 4b) are provided via an alternate switching circuit to the output of the tuner (1). connected. The speaker frequency filtering system according to claim 1, characterized in that the alternative switching circuit is implemented with connection diodes (D1, D2) connected in parallel to the inputs (4a, 4b) of the dual band filter (4), wherein the anode of the connection diodes L2) is connected to a power supply source (Vs) and to the common input point of the dual band filter (4), while the cathode of the first switching diode (D1) is connected via a capacitor (Cl) to one output point (IFI) of the tuning unit (1). Cathode D2) is connected via a capacitor (C2) to another output point (IF2) of tuner unit (1), via a collector resistor (R1) grounded to the cathode of the first switching diode (D1), to cathode of the second switching diode (D2) (R3) is connected to the first control input (Va) connected to the base circuit of the switching transistor (Q1). A speaker carrier frequency filtering system according to claim 1 or 2, characterized in that a switching diode (D3, D4, D5) is connected between the output terminals of the band filters (2, 3, 4) and connected to each other. connected in series, where the start and end point of the diode array is connected to the IF detnodulator (6) input via a capacitor (C3, C4) and a third control input (Ve) is connected to the anode (R9) of the third switching diode (D3) forming the diode array. , a second control input (Vb) is connected to the anode of the fourth switching diode (D4) and the cathode of the fifth switching diode (D5), and the emitter switching transistor (Q2) is grounded via a resistor (R6) to the anode of the fifth switching diode (D5) a collector connected to the second control input via a diode (D7) connected to the base circuit by an anode of a switching transistor (Q2) ttel (Vb), and its anode is connected to the third control input (Ve) via an additional diode (D8) connected to the base circuit.