JPS6327130A - Local oscillation circuit for tuner - Google Patents

Abstract

PURPOSE:To remarkably reduce cost by providing a VCO, a PLL circuit controlling it and a frequency multiplier multiplying the oscillated frequency from the VCO so as to eliminate the need for an expensive frequency divider. CONSTITUTION:The titled circuit is constituted by providing the VCO 26, a frequency divider 30 frequency-dividing its oscillated signal OS, a programmable divider 32, the PLL circuit 24 controlling the VCO 26 while using the signal subjected to frequency-division and the frequency muitiplier 28 multiplying the frequency of the signal OS and giving an output of the local oscillation signal. Thus, in giving an output of a 1st local oscillation signal LO1 having a frequency of 2.05-2.85GHz from the multiplier 28 having a multiplication number, e.g. 2, the frequency of the signal OS from the VCO 26 is 1.025-1.425GHz. Then part of the signal OS is inputted to the circuit 24 for the control purpose. Thus, a general-purpose frequency synthesizer IC or the like is used for the circuit 24. Then no expensive frequency divider for the high frequency operation is required.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a local oscillation circuit for a tuner, which is used, for example, as a first local oscillation circuit of a double-super one-type television tuner.

[Conventional technology]

FIG. 2 is a block diagram showing an example of a double super one type television tuner. The high frequency signal RF of the television broadcast manually input from an antenna etc. is amplified by the high frequency amplifier 2 and supplied to the first mixer 6, where the frequency is converted based on the second local oscillation signal Lo+ from the first local oscillation circuit 4. By doing so, the first intermediate frequency signal IFI is obtained. Then, the first intermediate frequency signal T F I is supplied to the second mixer 12 via the first intermediate frequency amplifier/filter 8,
There, the frequency is again converted based on the first local oscillation signal LO from the second local oscillation circuit 10 to obtain a second intermediate frequency signal IF2, which is then passed through the second intermediate frequency amplifier 14 to the next stage. We are trying to supply it to

In such a TV tuner, for example, an all-band tuner has a wide range (for example, 50 to 850 MHz).
In order to process the high frequency signal RF of z) all at once and with as little distortion, image disturbance, etc. as possible, the frequency of the first intermediate frequency signal IF is selected to be around the 2GH2 band, for example.

When the first intermediate frequency signal IF+ is brought to the 2 GHz band, the first local oscillation circuit 4 of the conventional frequency synthesizer type generates the first local oscillation signal of the 2 GHz band using a voltage controlled oscillator (VCO) as shown in the figure. LO, is oscillated, and a part of it is divided by a frequency divider (prescaler) 20 to a frequency that can be compared with a reference signal and is supplied to the PLL circuit 18 as a feedback signal. In this case, the band of the high frequency signal RF to be received is set to 50 to 85 as described above.
0 MHz, and the first intermediate frequency signal IF is 2 GHz, the voltage controlled oscillator 16 has a frequency of 2.05 to 2.85 GHz.
A variable width in the cell is required.

Now, if the reference signal for phase comparison is several KHz and a general-purpose frequency synthesizer IC (including a frequency divider, PLL circuit, and programmable divider for several hundred MH2 input) is used, the above 2°05~ Another frequency divider is required to reduce the 2.85 GHz signal LO to several hundred MHz.

Note that the programmable divider 21 receives, for example, a reference signal C for shifting data from the microcomputer 22.
K, a frequency setting signal DA for channel selection and a signal LD for transferring data converted from serial to parallel by a shift register to a several-bit data latch are supplied, and the PLL circuit 18 operates based on these signals. This is for supplying the voltage controlled IIII oscillator 16 with a tuning voltage (2) for control.

[Problem that the invention seeks to solve]

In the conventional first local oscillation circuit 4 as described above, the frequency of the voltage controlled oscillator 16 is, for example, 2°05 to 2.85.
Since the frequency is as high as GHz and has a wide variable range, it is difficult to manufacture the oscillator 16, and it is difficult to obtain a sufficient C/N.

Another problem is that an expensive frequency divider 20 that operates in a high frequency band of 2 GHz to 3 GHz is required.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a local oscillation circuit for a tuner that can be used, for example, in the first local oscillation circuit as described above, and does not have the problems of the conventional ones.

Means for Solving Problem C] The tuner local oscillation circuit of the present invention includes a voltage controlled oscillator, a PLL circuit that controls the voltage controlled oscillator using an oscillation signal from the voltage controlled oscillator, and a A frequency multiplier that multiplies the frequency of the oscillation signal and outputs it as a local oscillation signal.

[Effect]

The oscillation signal from the voltage controlled oscillator is multiplied by a frequency multiplier to create a local oscillation signal of a predetermined frequency. The oscillation signal before multiplication from the voltage controlled oscillator is fed back to the PLL circuit and used for control. Therefore, there is no need for a frequency divider that operates at a high frequency, and moreover, the oscillation frequency of the voltage controlled oscillator is low and its absolute variable range is narrow.

〔Example〕

FIG. 1 is a block diagram showing a local oscillation circuit according to an embodiment of the present invention. This local oscillation circuit 40 includes a voltage controlled oscillator (VCO) 26, a frequency divider 30 and a programmable divider 32 for dividing the frequency of the oscillation signal OS from the voltage controlled oscillator 26, and a frequency-divided signal. a PLL circuit 24 that controls the voltage controlled oscillator 26;
It includes a frequency multiplier 28 that multiplies the frequency of the oscillation signal O8 from the voltage controlled oscillator 26 and outputs it as a local oscillation signal. Note that the programmable delayer 32 is controlled by a microcomputer 34 as in the case of FIG. 2 above. Further, (2) is a tuning voltage for controlling the voltage controlled oscillator 26 as in the above case.

A more specific example of the local oscillation circuit 40 will be described using a case where it is used instead of the first local oscillation circuit 4 of a tuner as shown in FIG. 2, for example. The frequency multiplier 28 can be composed of, for example, a diode doubler, and from this frequency multiplier 28, for example, 2.05 to 2.8 as described above
When outputting the first local oscillation signal LO of 5 GHz,
The frequency of the oscillation signal OS from the voltage controlled oscillator 26 is preferably 1°025 to 1.425 GHz.

A part of the oscillation signal OS, which is a fundamental wave (that is, before multiplication), is input to the PLL circuit 24 and used for control. Therefore, as the PLL circuit 24, the PLL circuit 1
As in the case of No. 8, a general-purpose frequency synthesizer IC or the like (with a built-in programmable delayer and PLL circuit) can be used.

Therefore, according to the above-described local oscillation circuit 40, the expensive frequency divider 20 that operates at a high frequency as in the conventional circuit is not required, so that a significant cost reduction is possible. This is because frequency multiplier 28 is much easier and cheaper to manufacture than frequency divider 20.

Moreover, since the oscillation frequency of the voltage controlled oscillator 26 is low and its variable range is narrow, it becomes easy to design and manufacture the voltage controlled oscillator 26, and its output level can also be maintained over the entire band. Now you can get enough
Furthermore, it can be expected that the C/N will also improve.

Note that the multiplication number in the frequency multiplier 28 is not necessarily limited to the above-mentioned double, and various values may be used depending on the frequency of the desired local oscillation signal, the voltage controlled oscillator 26, the PLL circuit 24, etc. to be used. can be selected.

In addition, 1. Although the example in which the local oscillation circuit 4o is used as the first local oscillation circuit of a double super one-way TV tuner has been described above, the local oscillation circuit 40 can also be used for other local oscillation circuits. Of course, it is possible to do so.

〔Effect of the invention〕

As described above, according to the present invention, an expensive frequency divider for high frequencies is not required, so that costs can be reduced. Furthermore, since the oscillation frequency of the voltage controlled oscillator is low and its variable range is narrow, it is expected that the design and manufacture of the oscillator will become easier and the C/N will be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a local oscillation circuit according to an embodiment of the present invention. FIG. 2 is a block diagram showing an example of a double super one type television tuner. 4... First local oscillation circuit, 16.26... Voltage controlled oscillator, 18.24... PLL circuit, 20. ... Frequency divider, 28 ... Frequency multiplier, 40 ... Local oscillation circuit according to the embodiment, IF, ... First intermediate frequency signal, LO,
, ., first local oscillation signal.

Claims (1)

[Claims] (1) A voltage controlled oscillator, a PLL circuit that controls the voltage controlled oscillator using an oscillation signal from the voltage controlled oscillator, and a frequency multiplier that multiplies the frequency of the oscillation signal from the voltage controlled oscillator and outputs it as a local oscillation signal. A local oscillation circuit for a tuner, characterized by comprising: