JPS6028330A - Double superheterodyne tuner - Google Patents

Abstract

PURPOSE:To obtain the 2nd IF output signal which is highly stable by detecting the difference of a fundamental oscillating frequency of the 2nd local oscillating circuit and an oscillating frequency of the 1st local oscillating circuit to control the 1st local oscillating frequency by a PLL circuit. CONSTITUTION:A multiplier 9 doubles a frequency of an oscillator 10. In receiving a CATV signal of 50-450MHz, when the 1st IF signal frequency is 600MHz, the 1st local oscillating frequency is 650-1,050MHz and when the 2nd IF signal frequency is 62MHz, the oscillating frequency of the local oscillator 10 is 331MHz. The difference between the 1st local oscillating frequency and the oscillating frequency of the oscillator 10 is 319-719MHz by a mixer 11, which attains the frequency division by a fixed frequency divider 12 and the control of the oscillating frequency of the 1st local oscillating circuit 3 via the PLL circuit 13.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a tuner for receiving television signals, and particularly to a double superheterodyne tuner suitable for receiving all cAry signals.

[Background of the invention]

A double superheterodyne tuner that receives a CATV signal and converts it into an RF signal of an idle channel will be described with reference to FIG.

FIG. 1 is a block diagram for explaining the entire structure of a general double superheterodyne inch.

In FIG. 1, 1 is an RF multiplied signal input terminal, 2 is a first mixer, 3-digit first local oscillation circuit, 4 is a band pass filter, 5 is an 11F signal amplifier, 6 is a second mixer, and 7 is a Second
In the local oscillation circuit, 8 is a second IF signal output terminal.

The RF multiplied signal input to the RF signal input terminal 1 is converted into an 11F signal by the first mixer 2 by the first local oscillation circuit 3, and selectively amplified by the bandpass filter 4 and U1g1 IF signal amplifier 5. Thereafter, the signal is converted into a 21F signal by the second mixer 6 using the oscillation signal of the second local oscillation circuit 7, and is outputted from the output terminal 8.

The desired RF signal is selected by selecting the oscillation frequency of the first local oscillation circuit 6, and the 11th F signal frequency is normally set to a higher frequency than the RF signal frequency to be received. The second IF signal frequency is normally set to 3 channels (including 2 channels) in CATV reception in the United States.

In a double superpeterodyne tuner, in order to obtain a stable 21st F signal, the oscillation frequency of the first local oscillation circuit 3, the oscillation frequency of the second local excavation circuit 7, and the passband center frequency of the bandpass filter 4 must be set respectively. They need to be stable or otherwise vary equally.

Therefore, in order to obtain a stable 21st F signal, if the first local oscillation circuit 6 is accurately controlled by a PLL circuit or the like,
The frequencies of the bandpass filter 4 and the second local oscillation circuit 7 must also be made highly stable. For example, if the first local oscillation frequency is about 10H at maximum, the second local oscillation circuit 7
By stabilizing the bandpass filter 4, the first local oscillation frequency can be directly detected and controlled by the PLL circuit.

However, in this case, for example, the first IF signal frequency is 2~
5 (Jz), the first local oscillation frequency also becomes high, which makes direct frequency division difficult and has the disadvantage that PLL control becomes impossible.

In addition, when the first local oscillation frequency is controlled by the PLL circuit using the difference frequency between the first local oscillation circuit 3 and the second local oscillation circuit 7, the frequency stability of the bandpass filter 4 and the second local oscillation circuit 7 is the same. In addition, the first
There are problems such as the frequency difference between the local oscillator circuit 3 and the second local excavation circuit 7 being zero, and if the 21st F signal frequency is set to 3 channels, it is not possible to distinguish between 2 channels and 4 channels. The drawback was that it was difficult.

[Purpose of the invention]

The object of the present invention is to eliminate the drawbacks of the above-mentioned conventional technology, to enable stable control of the first local oscillation frequency f by a PLL circuit, and to
An object of the present invention is to provide a double superheterodyne chainer capable of obtaining a highly stable 21st F signal output.

[Summary of the invention]

According to the present invention, the above object is to configure the second local oscillation circuit with an oscillator and a multiplier that multiplies the oscillation frequency to produce an oscillation output, and to combine the basic oscillation frequency of the oscillator with the first local oscillation circuit. PLL by detecting the frequency difference with the oscillation frequency
This is achieved by controlling the first local oscillation frequency by a circuit.

[Embodiments of the invention]

FIG. 2 is a block diagram showing one embodiment of the present invention.

In FIG. 2, elements having the same functions as those in FIG. 1 are designated by the same numbers, and explanation thereof will be omitted.

Also, in the same figure, 9 is a multiplier, 10 is an oscillator, and 11 is a multiplier.
1 is a third mixer, 12 is a fixed divider, and 16 is a PLL circuit.

In FIG. 2, a multiplier that doubles the oscillation frequency of the oscillator 10 is used as the multiplier 9.

When receiving all CATV signals of 50 to 450 dHz, if the 11th F signal frequency f is 600 MHz, the first local oscillation frequency is 650 to 105105 O, and if the 21st F signal frequency is f 62 MHz, the oscillation frequency of the local oscillator 10 is It becomes 331MH2. Therefore, if we calculate the difference between the first local oscillation frequency and the oscillation frequency of the oscillator 10 in the fifth mixer 11, we get 319 to 719 MH2. The oscillation frequency of the first local oscillation circuit 3 can be controlled.

Another embodiment of the present invention will be described with reference to FIG.

FIG. 3 is a block diagram showing another embodiment of the present invention.

In FIG. 3, elements having the same functions as those in FIG. 2 are given the same numbers, and explanations thereof will be omitted. In the figure, 14 is a duplexer.

In the double superheterodyne system shown in FIG.
, the bandpass filter 4 and the i-th IF amplifier 5 are input to the second mixer 6, and the signal having the frequency difference between the second local oscillation signal and the signal from the oscillator 10 is multiplied by a second rp by the splitter 14. The signals are differentiated and extracted, and if the signal level of the signal is low, it is amplified or frequency-divided by a fixed divider 12, and the oscillation frequency of the first local oscillation circuit 3 is controlled via a PLL circuit 13.

〔Effect of the invention〕

According to the present invention, in a double superheterodyne CATV reception tuner that converts a television signal into an fRF signal, the 11th F signal frequency can be raised to a high frequency, and even when it is difficult to directly divide the first local oscillation frequency. 1 local oscillation frequency' (can be stably controlled by the i-PLL circuit,
A highly stable external 21st F signal output can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram for explaining a general double superheterodyne tuner, and FIGS. 2 and 3 are block diagrams showing embodiments of the present invention. 1... RF signal input terminal 2... First mixer 3...
・First local oscillation circuit 4...Band pass filter 5・
・Jth IF signal amplifier 6 ・Second mixer 7'・
... Second local oscillation circuit 8 ... 21st F signal output terminal 9 ... Multiplier 10 ... Oscillator 11 ... Sixth mixer 12 ... Fixed frequency divider 13 ...
・PLL circuit 14...Branch secrets Figure 2 Figure 3

Claims (1)

[Claims] 1) A first mixer that converts the frequency of an RF input signal into an oscillation output from a first local oscillation circuit and outputs the resultant signal; In an f-pull superheterodyne tuner that includes a second mixer that converts the frequency of an oscillation output and outputs the same, the second local oscillation circuit is a multiplier that multiplies the oscillation frequency and outputs the oscillation output. a detection means for detecting and outputting a frequency difference between the fundamental oscillation frequency of the oscillator and the oscillation frequency of the first local oscillation circuit; A double superheterodyne tuner comprising a PLL (phase locked loop) circuit that controls the oscillation frequency of an oscillation circuit.