JPS6059770B2 - Bias circuit of tuning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a channel selection device for a television receiver.

Conventionally, an example of using a surface acoustic wave element (hereinafter abbreviated as "AW element") as an automatic tuning device for a television receiver equipped with an electronically tuned tuner is known. Fig. 1 shows its configuration. In the figure, 1 is an electronic tuning tuner, 2 is a SAW element, 5 is a detection circuit, 4 is an amplifier circuit, 5 is a waveform shaping circuit, 6 is a frequency divider circuit, 7 is a programmable counter, and 8 is a A tuning voltage sweep circuit, 9 a keyboard switch, 10 an encoder, and 11 a display device.
Here, the SAW element 2 will be explained using FIG. 2.
The SAW element 2 has an input electrode 12 and output electrodes 13 and 14 connected to each other arranged on a voltage-sensitive substrate such as LiNbO3 or LiTaOa, and the local oscillation output supplied from the electronic tuner 1 to the input terminal 2a is input. It is input to the electrode 12. This is converted from an electrical signal to a surface wave at the electrode 12 and reaches the output electrodes 13 and 14. Here, the local oscillation signal becomes an electric signal again, but the output electrodes 13 and 14
are arranged at different distances from the input electrode 12, so the signals at both electrodes have a phase difference from each other.
Therefore, the signal at the output electrode 13 is V, ■Aejω''(ω■
2πff: frequency), the signal at the output electrode 14 becomes V2■Aejω("-T', where T is the delay time).

Since both electrodes 13 and 14 are connected to each other, the composite signal is V=V, +V2=Aejω ”+Aejω
(”-T).

The amplitude IVI of this is 1V1=A1ejω”+ejω゛”
Ichi'l Av/2 (1+cosωT), and this value is the maximum value when s ω=△π/T, that is, when Chi=N/T (N: an integer)/τ (N: an integer) Take the minimum value 0.

The frequency intervals Δf that take the maximum value are equal intervals.

Therefore, the passband of this SAW element 2 is the local oscillation frequency band of each television broadcasting band (VHF low band, ■HF high band, UHF band), for example, V
HF' low band (1~3Ch.) 150~162
MHzVHF' high band (4~12Ch.) 230
~276MHz open F band (13-62Ch.)
The passband is selected to be 4 MHz lower than the initial frequency of 530 to 824 MHz, and τ = 0.5.
When set to μSec, a frequency characteristic as shown in FIG. 3 can be obtained in decibel display.

The numbers surrounded by circles indicate the peaks corresponding to that channel. ■HF low band, ■HF high band, U
FIG. 4 shows a method of configuring a SAW element 2 used in a television receiver that receives broadcast waves in three bands of the HF band.

The reason why the two VHF band elements are connected in parallel is that they do not share each other's bandwidth, and the VHF band
This is because in the F tuner, its local oscillation output is output from the same location. Based on the above points, the operation of the channel selection device shown in FIG. 1 will be explained.

When a desired channel number to be selected is input to the keyboard switch 9, the number is converted into a binary code by the encoder 10 and preset in the programmable counter 7.
This is further sent to a display device 11 such as a channel number, and the channel number is displayed. When the channel number is input, the tuned voltage sweep circuit 8 starts voltage sweep. Apply this voltage to electronic tuner 1! and the local oscillation frequency gradually increases. When this output is input to the electrode 12 of the SAW element 2, the level of the local oscillation signal increases or decreases in accordance with the frequency characteristics of the SAW element 2 at the output of the SAW element 2. Then, by detecting four waves of this output using the detection circuit 3 and counting the number of peaks, it is possible to know how many broadcasting stations the signal has passed through and which station it is tuning to. Therefore, this signal is amplified by an amplifier circuit 4, converted into a pulse by a waveform shaping circuit 5, divided by 3 by a frequency divider circuit 6, and sent to a counter 7. The counter 7 counts down this pulse until the counter value reaches a predetermined value, for example V.
0 for HF low band, 3 for HF high band,
In the case of the UHF band, a sweep stop signal is generated when the voltage reaches 12, and when this signal is applied to the tuning voltage sweep circuit 8 and the sweeping of the tuning voltage is stopped, the tuning is completed. For example, when the third channel of the VHF' band is selected, the initial value of the counter 7 is 3, but when the local oscillation frequency reaches 162 MHz, as shown in FIG. As a result, the data in the counter 7 becomes 0, and the channel selection is completed. In such a tuning device, the power supply to the detection circuit 3 and the amplification circuit 4 is as shown in FIG. In FIG. 5, circuit blocks surrounded by dotted lines are a detection circuit 3, an amplifier circuit 4, and a waveform shaping circuit 5, respectively. Also resistance 1
7. A stabilized power supply circuit 16 composed of a Zener diode 18 and a capacitor 19 supplies power to the detection circuit 3 and the amplifier circuit 4 as power. This stabilized power supply 16 is designed to prevent fluctuations in the power supply (+B) line, ripples, etc.
This is provided to reduce the influence of noise, etc., prevent noise signals from the power supply line from being mixed into the minute signal output from the detection circuit 3, and extract a stable signal.

Also, the stabilized power supply 16 supplies power to the amplifier circuit 4 as a preamplifier of the waveform shaping circuit 5, not only to prevent noise from the power supply line to the amplifier circuit 4, but also to prevent noise from the power supply line when the power supply fluctuates. This is to prevent fluctuations in the potential across the detector circuit 3 (the potential difference between the output bias voltage of the detection circuit 3 and the input bias voltage of the amplifier circuit 4). Incidentally, even in a circuit configured in this manner, it takes time for the potentials across the coupling capacitor 15 to converge when the power is turned on.

Further, since all of the driving current for the amplifier circuit 4 is supplied, the load on the stabilized power supply 16 becomes heavy, which causes problems such as affecting the performance against power supply fluctuations. Furthermore, the output bias voltage of the amplifier circuit 4 is protected against power fluctuations by the stabilized power supply 16, but since the waveform shaping circuit 5 is directly driven by the power supply line, the threshold voltage is protected against the influence of power fluctuations. receive. Alternatively, there have been other problems, such as the need to provide a separate stabilizing voltage or to strengthen the driving capability of the stabilized power supply 16. An object of the present invention is to eliminate the drawbacks of the prior art described above, improve the stability of operation, and provide a bias circuit equipped with a stabilizing power supply circuit of relatively simple circuit scale. It is on offer.

The present invention will be explained in detail below using examples.

FIG. 6 is a circuit diagram showing one embodiment of the present invention. In the figure, the circuit connection between the detection circuit 3 and the stabilized power supply 16 is the fifth one.
Same as the figure. Also, 51-56 and 59-63 are resistances,
57 and 58 are operational amplifiers. Here, the resistors 51 to 56 and the operational amplifier 57 constitute a non-inverting type amplifier circuit 4, and the resistors 59 to 63 and the operational amplifier 58 constitute a non-inverting type waveform shaping circuit 5. Incidentally, in the figure, the input bias point that determines the operating point of the amplifier circuit 4 is determined by the voltage divided by the resistor 51 and the resistor 52.

Power is supplied from a stabilized power supply 16. Similarly, the comparison voltage that determines the threshold voltage of the waveform shaping circuit 5 is a voltage divided by a resistor 59 and a resistor 60 supplied from the stabilized power supply 16, which is inverted by an operational amplifier 58 via a resistor 62. It is added to the input side. Therefore, the detection circuit 3 stably driven by the stabilized power supply 16
The detected output signal is transmitted to the resistor 54 via the coupling capacitor 15, and is applied as an input signal to the non-inverting input side of the operational amplifier 57.

Furthermore, as mentioned above, the stabilized bias voltage divided between the resistor 51 and the resistor 52 is applied to both the non-inverting input side via the resistor 53 and to the inverting input side via the resistor 55. The operating point of the operational amplifier 57 which is operated by the power supply is determined and operated. Therefore, the amplifier circuit 4 is amplified by the amplification factor determined by the resistance ratios between the resistors 55 and 56 and between the resistors 54 and 53. Next, this amplified detection signal is applied as an input signal to the non-inverting input side of the operational amplifier 58 of the waveform shaping circuit 5 via the resistor 61.

Further, as described above, the threshold comparison voltage divided and stabilized into the resistor 59 and the resistor 60 is applied to the inverting input side via the resistor 62. Therefore, the waveform shaping circuit 5 shapes the waveform by the so-called Schmitt trigger circuit operation with a transition width (having hysteresis characteristics) determined by the resistance ratio of the resistors 61 and 63. FIG. 7 is a circuit diagram showing another embodiment according to the present invention.

In the figures, the same parts are indicated by the same numbers and will therefore be omitted. Here, the detection output signal of the detection circuit 3 is applied to the inverting input side of the operational amplifier 57 via the coupling capacitor 15 and the resistor 54, and the stabilized bias is inverted as in the embodiment shown in FIG. , is applied to both non-inverting inputs. Therefore, this amplifier circuit 4 has a resistor 56.
The signal is inverted and amplified by the amplification factor determined by the resistance ratio of the resistor 54 and the resistor 54. Next, this amplified detection signal is transmitted to the resistor 6
2 to the inverting input of the operational amplifier 58, and the stabilized comparison voltage is applied to the non-inverting input, contrary to the previously described embodiment of FIG.

Therefore, this waveform shaping circuit 5 includes a resistor 61 and a resistor 6.
The waveform is shaped by a so-called inverted Schmitt trigger circuit operation with a transition width (having hysteresis characteristics) determined by a resistance ratio of 3. As described above, according to the present invention, by driving only the input bias circuits of the waveform shaping stage and the waveform shaping preamplification stage with the stabilized power supply, the entire circuit stage can be driven almost simultaneously with the stabilized power supply, or More stable operation can be achieved. In addition, the current capacity of the stabilized power source does not need to flow through the entire circuit as in the prior art, so it can be reduced, making it possible to unify the stabilized power source and simplify the circuit.

As can be seen from the examples, the operation of the amplification stage and waveform shaping stage is controlled by the bias voltage of the input bias circuit, and it is easy to realize a circuit configuration in which the amplifier stage and the waveform shaping stage are driven by the same stabilized power supply as the detection stage. Therefore, even when a coupling capacitor is interposed as in the embodiment, the potentials across the coupling capacitor converge quickly when the power is turned on, and malfunctions immediately after the power is turned on can be easily prevented.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of a channel selection device using a SAW element, Fig. 2 is a pattern diagram showing the electrode structure of the SAW element, Fig. 3 is a characteristic diagram showing the frequency characteristics of the SAW element,
FIG. 4 is a pattern diagram showing a specific electrode structure used in the SAW element of FIG. 1, FIG. 5 is a circuit diagram for explaining a conventional bias circuit, and FIG. 6 is a diagram of a bias circuit according to the present invention. FIG. 7 is a circuit diagram showing another embodiment of the bias circuit according to the present invention. 1: Electronic tuner, 2: SAW element, 3: Detection circuit, 4
: amplifier circuit, 5: waveform shaping circuit, 15: coupling capacitor.

Claims (1)

[Claims] 1. An electronically tuned tuner having a voltage-controlled local oscillator, a surface acoustic wave filter whose output signal is input to the electronically tuned tuner, a detection amplification means for detecting an output signal of the surface acoustic wave filter, and the electronically tuned tuner. A channel selection device comprising a sweeping means for sweeping the local oscillation frequency of the detector, a waveform shaping means for converting the output signal obtained by the detection amplification means into a pulse waveform, and a counter stage for counting the pulse output signal of the waveform shaping means. , comprising a stabilized power supply circuit that drives both the detection amplification means and the waveform shaping means, and only the input bias circuits of the waveform shaping means and the waveform detection amplification means are supplied with current from the stabilized power supply circuit. A bias circuit for a tuning device characterized by: