JPS5810019B2 - VHF/UHF tuner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a VHF-UHF tuner, and its purpose is to reduce the number of variable capacitance diodes (hereinafter referred to as varactors) and to provide a VHF-UHF tuner that does not require tracking adjustment. It is on offer.

A conventional VHF-UHF tuner has a configuration as shown in Figure 1, in which the vHF signal is transmitted from input terminal 1 to antenna input circuit 2.
5, unnecessary signals such as intermediate frequency (hereinafter referred to as IP) signals and FM signals are removed and the signal is passed through the single tuning circuit 26.
is input.

The single tuning circuit 26 is equipped with a varactor for signal selection and a switching diode for high band and low band switching, so that it can tune to the reception frequency.

The output from the single-tuned circuit 26 is input to the high-frequency amplifier circuit 27, which is controlled by the AGC signal from the terminal 37 so as to obtain a desired degree of amplification, and the amplified signal is input to the double-tuned circuit 28. is input to.

The double-tuned circuit 28 includes two varactors and two switching diodes, and removes the image signal tuned to the received signal and other unnecessary signals, and prevents the oscillation signal from the local oscillation circuit 30 from leaking to the antenna side. To prevent.

The output of the double-tuned circuit 28 is input to a mixing circuit 29, and an oscillation signal from a local oscillation circuit 30 equipped with a varactor, a switching diode, etc. is input to the mixing circuit 29, and a 1F signal is taken out from the terminal 22. Ru.

The varactors of each circuit are controlled by the tuning voltage from the terminal 39, and the switching diodes are controlled by the switching voltage from the terminal 40.

Next, the UHF signal is input to the single tuning circuit 31 from the terminal 2, and a tuning circuit including a varactor removes unnecessary signals and selects a received signal.

The selected signal is input to a high frequency amplifier circuit 32 whose amplification degree can be controlled by an AGC signal from a terminal 38, and is input to a double tuning circuit 33 after being amplified.

The double tuning circuit 33 includes two varactors and removes the image signal and unnecessary signals tuned to the received signal, thereby preventing the oscillation signal from the local oscillation circuit 35 from leaking to the antenna side.

The output from the double-tuned circuit 33 is input to a mixing circuit 34, and an oscillation signal from a local oscillation circuit 35 whose frequency can be changed by a varactor is input to the mixing circuit 34, which performs frequency conversion and outputs an IP times signal.

The IF signal is input to the IF amplifier circuit 36 and amplified.
The signal is input to the HF mixing circuit 29, amplified to a desired level, and taken out from the IFL element 22.

When receiving UHF, the VHF local oscillation circuit 30 is not supplied with an operating voltage and stops operating, and the vHF mixing circuit 29 simply works as an IP amplifier, and if sufficient amplification gain can be obtained with the mixing circuit 29, IP amplifier 1 The benefit circuit 36 becomes unnecessary.

In the VHF-UHF tuner of the conventional circuit described above, VHF
Four varactors with uniform characteristics (with capacitance deviation within ±2% to ±5% over the entire tuning voltage range) are required, and in terms of cost, they are the most expensive components in Chuyo. In addition, tracking adjustment between circuits using four varactors becomes difficult.

Varactors have low Q, lack of selectivity especially in UHF, and NF
There were drawbacks such as deterioration of the material.

The present invention solves the above-mentioned drawbacks by using two varactors in a VHF-UHF tuner for reception. An embodiment of the present invention is shown in a block diagram in FIG. 2, and in a detailed circuit diagram in FIG. To explain using the reception frequency of
The input filter circuit 3 has capacitors C1,
C3 to C5, C7 to C9, a 40 to 220 MHz bandpass filter composed of coils L1 to L7, and diodes D1. D2 resistor R1, R2, capacitor C2゜C6
, C15tc27. It consists of C28 and coils 151-16, and when receiving HF, the voltage from terminal 17 (vc
higher voltage) causes diode D1. D2 is turned off and the VHF signal passes through without attenuation, and when receiving UHF, the diode D1. A switch circuit in which D2 is turned on and the VHF signal is attenuated, and capacitors C1o to C13
, consisting of coils L8 to L11, 88 to 110MH
A band reject filter that passes the signal of z,
It is composed of a capacitor C14, coils L12 to L14, and a low pass filter having a cutoff frequency of 360 MHz, and the VHF signal is input to the next stage attenuation circuit 5 using a pin diode.

The UHF band signal is input from the terminal 2 to the input filter circuit 4, and the input filter circuit 4 is connected to the capacitors C16 to C1.
8,C2o.

C22, consists of coils L17 to L20, 450M
A bypass filter whose cutoff frequency is near Hz, diodes D3 to D, and a capacitor C19°C21jC
89, coil L22jL23, resistance R3, R4゜R39
When receiving UHF, the voltage v from terminal 18 is
c) causes diode D3. D4 is OFF
, diode D5 turns on, the UHF signal passes,
When receiving vHF, diode D3. D4 is turned on, diode D5 is turned off, and the UHF signal is output.

Switch circuit, capacitors C24 to C26, and coils
21 and a bypass filter having a cutoff frequency of 360 MHz, and the passed UHF signal is input to the attenuation circuit 5 at the next stage.

The attenuation circuit 5 includes pin diodes D6 to D8 and resistors R5 to
AGC consisting of R9, capacitors C29 to C33, coil L24, and transistor Q1, and input from terminal 19.
A signal is input to the base of transistor Q1, and if the signal level is disturbed, the pin diode D is input by the AGC signal.
The resistance values of 6 to D8 change to lower the signal level, and a signal at a constant level is always input to the broadband amplifier circuit 6.

The wideband amplifier circuit 6 is composed of one IC and has a power of 40 to 900
It amplifies MHz signals with an amplification factor of approximately 20 dB.
The amplified signal is input to the first mixing circuit 7.

The first mixing circuit 7 uses two image-reject type balanced diode mixers, and may be a single-balanced or double-balanced diode mixer.

), one mixer inputs an oscillation signal with a /4 phase lead from the directional coupler T2 to the primary winding of the transformer T4, and outputs the VHF signal (
The 11th F signal is taken out from the middle point of the secondary winding of transformer T4, and the other mixer receives an oscillation signal whose phase is delayed by 〒/4 from the primary winding of transformer T5. , V from the junction point of diode DlljD12
Transformer T4 to which HF signal (UHF signal) is input
The 11th F signal of each mixer is extracted from the secondary winding of
9, a resonant circuit consisting of a coil L26 removes unnecessary signals and guides them to the directional coupler T3.

For example, in the directional coupler T3, the transformer T4
If the signal input from the transformer T is one phase ahead, then the signal input from the transformer T is one hundred phases behind.

Further, in each signal, a regular IF multiplied signal obtained by converting the received wave by the respective mixer and an image signal obtained by converting the image wave are overlapped.

If the phase of the signal output to the resistor R11 connected to the directional coupler T3 is based on the signal input from the transformer T4, a phase difference of Σ is further generated by the directional coupler iT3, so that This results in a phase difference of π.

For this reason, each normal IF multiplied signal has an opposite phase, is canceled and is not output, and each image signal has the same phase, and only the image signal is output to the resistor R11.

On the contrary, the phase of the signal output to coil L39 is
The normal IF multiplied signal is outputted as having the same phase, the image signal has the opposite phase and is canceled, and only the normal IF multiplied signal is outputted to the coil L39.

As mentioned above, the signal from the local oscillator is connected to the directional couplers T2 and T3.
When the composite sum is taken through , the image components cancel each other out and the image components are removed.

The oscillation signal input to the first mixing circuit 7 is transmitted through the oscillation transistor Q2. Q3, resistor R12~R20, coil L27~
L29, capacitor C40"C43, C45~C30C
62, C63, c67, diode D13tD14 as a tuning variable capacitance element. Tab TA2 for frequency adjustment,
It is oscillated by the first local oscillation circuit 8, which is made up of a coil TA1 that takes out the oscillation output, and its oscillation frequency is controlled by the diode D.
From the variable range of 13tD14, the ratio between the maximum value and the minimum value must be Fmax/Fm1n≦2, and
Considering the frequency of the UHF-VHF signal, the frequency of the 11th F signal is below 54 MHz, between 216 and 470 MHz,
If the value is not 890 or more, the UHF-VHF signal will pass through and cause a beat disturbance, which is not preferable.

Therefore, if the 1F frequency is determined to be 373MHz, Ft
From the relationship v+Fif=Fosc, Ftv: Television signal frequency Fif: IF times signal frequency Fosc: Oscillation frequency The oscillation frequency is 427 to 589 MHz when receiving VHF, and 421.5 to 631.5 MHz when receiving UHF (here, the oscillation frequency is The lower frequency is the second one, which will be explained later.
This is because harmonic components are used.

), which satisfies the oscillation conditions.

To explain the principle of the first local oscillation circuit 8, it constitutes a push-pull oscillation circuit, and the oscillation conditions are transistor Q2. Q3
, feedback capacitor C419c50, diode D1
3#D14, capacitor C40, C45°C46, C4
9. Determined by the coil L28, if these satisfy the oscillation conditions for the fundamental wave and the second harmonic, or if the transistor Q2. If Q3 has large distortion characteristics, coil L28.
The voltage mode of the fundamental wave of TA1 is the coil L28. The voltage is zero at the center of TA1 and highest at both ends, and the voltage mode of the second harmonic is the coil L28. The voltage is high at the center and both ends of TA1, and becomes zero between the center and both ends.

Therefore, the fundamental wave component is extracted from the end of the coil TA1, and the second harmonic is extracted from the center of the coil L28.

The oscillation output of the first local oscillation circuit 8 is the coil L28 and T
The vHF oscillation signal is extracted from Al and input to the filter 12, and passes through a filter consisting of coils L35 to L37 and a capacitor C59 to remove unnecessary signals.

In addition, the UHF oscillation signal is generated by coil L38 and capacitor C5.
9 to C61 to remove unnecessary signals mainly the fundamental oscillation frequency components.

The output of the filter 12 is a switching diode D1
5 to D18, choke coil L32jLaa, capacitor C55, and resistor R25, and when a positive voltage is applied to terminal 20, diode D1
7. D18 is on, diode DI5. D16 is turned off, the signal for VHF reception is input to the first mixing circuit 7, and the signal for UHF reception is grounded through the capacitor C55.

Furthermore, when a positive voltage is applied to the terminal 21, the diode D1
5 to D18 are reversed, and only the signal for UHF reception is input to the first mixing circuit 7.

The signal for VHF reception or the signal for UHF reception that has passed through the switch circuit 10 is passed through the directional coupler T of the first mixing circuit @7.
2 and mixed by diodes D9 to D12, only the desired channel signal is converted to the 11F frequency by the first local oscillation signal corresponding to the desired channel,
This means that the first mixing circuit 7 has performed signal selection.

The 11F amplification circuit 13 extracts the selected 11F signal from the directional transformer T3 and inputs it to the 11P amplification circuit 13. Helical resonator on the input side consisting of L4o, transistor Q4, and resistors R28 to R3
o1 coil L41. The coil L41 and the capacitor C68 are connected between the coil L4o and the transistor Q4 of a helical resonator that is composed of a bandpass filter consisting of capacitors C7o and C73, a coil L42L43, and a capacitor C711C721c88, and has a bandwidth of 4.5 MHz.
is set up to perform impedance matching, and the first
The 1F signal is amplified and input to the second mixing circuit 14.

The second mixing circuit 14 includes an impedance matching coil L44. Consisting of an L5o1 capacitor C749C75, a diode D2ON injection coil TA3 for mixing, a resistor R34A coil L47, and a capacitor C8°, the oscillation signal from the second local oscillation circuit 15 and the 11F signal are mixed and the second IF signal is output to the second IF. The signal is input to the amplifier circuit 16.

The second local oscillation circuit 15 is a transistor Q5A resistor R31
~R33, coils L45~L46. Capacitor C76~
C79, ca6. Consists of C90, C91, and tab IA4 for frequency adjustment, and has a predetermined frequency of 327.25.
A fixed oscillation is performed at MHz and the oscillation signal is sent to the second mixing circuit 14.
A second IF signal of 45.75 MHz is input from the second mixing circuit 14 to the second IF amplifier circuit 16.

The second mixing circuit 16 includes a helang transistor Q6 and a resistor R35.
R38, capacitor C81~C85+C87, coil L
489L49, amplifies the signal to a predetermined level and passes it through a 45.75MHz bandpass filter to terminal 2.
The second IF signal is taken out from 2.

Although the input filter circuit 3 uses a band-pass filter, a low-pass filter may also be used and can be used without major problems.

According to the invention as shown above, the tuning varactor is the first
Since only two out of two varactors can be used in the local oscillation circuit, there is no need to collect varactors with uniform characteristics in sets of four, and there is no need for tracking adjustment.Also, since AGC is performed separately from the amplifier circuit using pin diodes, there is no need for mixing. Modulation can be improved.

Since a varactor is not used in the high frequency signal circuit of JHF, the Q does not become low and NF deterioration can be prevented. Also, when receiving UHF, the second high frequency component of the basic signal oscillated by the first local oscillation circuit is used, so it is especially suitable for UHF. It can be used for both vHF and U-F without using a local oscillation circuit, and inputs the signal advanced and delayed by /4 to the first mixing circuit, extracts the IF times signal from each, and calculates the combined sum. Since the 11th F signal is finally obtained, extremely large effects such as being able to prevent the influence of image interference waves are achieved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional VHF-UHF tuner, FIG. 2 is a block diagram showing a VIF-UHF tuner according to the present invention, and FIG. 3 is a detailed circuit diagram. 1.2, 17, 18, 19, 20, 21, 22...
...Terminal, 3, 4...Input filter circuit, 5.
...Attenuator, 6...High frequency amplification circuit, 7
......First mixing circuit, 8...First local oscillation circuit, 10...Switch circuit, 12...
Filter, 13...First intermediate frequency amplification circuit, 1
4... Second mixing circuit, 15... Second local oscillation circuit, 16... Second intermediate frequency amplification circuit.

Claims (1)

[Claims] l The signal from the input filter circuit that separates the VHF signal and the UHF signal is input to an attenuator using a pin diode to perform AGC operation, and the signal that has reached an appropriate level is amplified by a wideband amplifier circuit to perform the first mixing. In addition to inputting the fundamental wave component signal oscillated by the first local oscillation circuit to the first mixing circuit when receiving the vHF signal, the UH
When receiving the F signal, the second harmonic component signal oscillated by the first local oscillation circuit is input to the first mixing circuit, and a predetermined first intermediate frequency signal is extracted and input to the first intermediate frequency amplifier circuit. After being amplified, the signal is input to the second mixing circuit, where it is mixed with the oscillation signal from the second local oscillation circuit to extract the second intermediate frequency signal, and the second intermediate frequency signal is input to the second intermediate frequency amplification circuit. A VHF-UHF tuner characterized by amplification.