JPH06216639A - Oscillation output circuit - Google Patents

Abstract

PURPOSE:To obtain an oscillation output circuit supplying the oscillation signal from an oscillator with high oscillation frequency to a prescaler of the succeeding stage with excellent isolation and at a low cost. CONSTITUTION:Between a local oscillator 13 with high oscillation frequency and a prescaler IC 14, a high-pass filter 22 which is composed of a coil 23 and a capacitor 24 is provided. The cutoff frequency is set lower than the frequency of the oscillation signal to be outputted from the local oscillator 13 and higher than the frequency of the signal to be outputted from the prescaler IC 14. Further, the side of the ground terminal of the coil 23 is directly connected with the side of the GND terminal of the prescaler IC 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillating output circuit for supplying an oscillating signal output from an oscillator to a circuit in the next stage. For example, a tuner having a PLL frequency synthesizer type tuning circuit, particularly an oscillating frequency It is suitable for use in a satellite broadcast receiving tuner (BS tuner) in which a high local oscillator is used.

[0002]

2. Description of the Related Art Conventionally, a satellite broadcast receiving tuner having a PLL frequency synthesizer type tuning circuit is constructed as shown in FIG. 2, and 1 is a 12 GHz band received signal from a parabolic antenna and is a 1 GHz band BS. An input terminal to which the BS intermediate frequency signal from the BS converter, which has been frequency-converted into an intermediate frequency signal, is input, 2 is a high-frequency amplifier that amplifies the input BS intermediate frequency signal, and 3 is a signal to prevent unwanted signal mixing. It is a high frequency band pass filter that passes only the BS intermediate frequency signal from the high frequency amplifier 2.

A mixer 4 mixes the BS intermediate frequency signal from the high frequency band pass filter 3 with an oscillation signal from a local oscillator, which will be described later, and frequency-converts it into a second intermediate frequency signal (hereinafter referred to as "IF signal"). Reference numeral 5 designates an IF amplifier for amplifying the IF signal taken out from the mixer 4, and 6 designates an I signal for eliminating unnecessary signals and passing only the IF signal from the IF amplifier 5.
F band pass filter, 7 is an IF amplifier that amplifies the IF signal again, 8 is an FM detector that performs FM detection of the IF signal from the IF amplifier 7, and 9 is an output terminal from which the FM detection output is derived.

Reference numeral 10 denotes an AGC detection diode that diode-detects the IF signal from the IF amplifier 7 to generate an AGC voltage. Reference numeral 11 amplifies the AGC voltage from the detection diode 10 and supplies it to the IF amplifier 5. Then, the gain of the IF amplifier 5 is controlled according to the AGC voltage, so that the input level to the FM detector 8 does not fluctuate due to the intensity of the received radio wave.

Reference numeral 12 denotes a PLL frequency synthesizer system tuning circuit portion, and 13 has an oscillation frequency of 1 GHz to
Local oscillator, relatively high at 2.6 GHz (in this case, VC
O), 14 is a prescaler with a division ratio of 1 / N ₀ (high-speed fixed) that lowers the frequency of the oscillation signal supplied from the local oscillator 13 via the amplifier 15 to the operating frequency at which the programmable frequency divider in the next stage can divide. 16) is a programmable frequency divider that divides the output from the prescaler 14 by a variable frequency division ratio 1 / N, and the variable frequency division ratio 1 / N is a channel selection microcomputer according to a channel selection operation. It is made variable by a data signal for frequency division ratio control supplied from a control terminal (not shown).

Reference numeral 17 is a reference oscillator (crystal oscillator) for outputting a reference signal having a constant frequency, and 18 is a fixed frequency divider for dividing the frequency of the reference signal supplied from the reference oscillator 17 by a division ratio 1 / N ₁ . , 19 are phase comparators for comparing the frequency-divided output from the fixed frequency-divider 18 and the frequency-divided output from the programmable frequency-divider 16 to detect the frequency shift, that is, the phase difference, the output of which is a low-pass filter. It is supplied to the local oscillator 13 through 20 and controls the oscillation frequency thereof. The oscillation signal of the local oscillator 13 whose oscillation frequency is controlled in this way is passed through the amplifier 21 to the mixer 4
To be supplied to.

Therefore, if the frequency division ratio 1 / N of the programmable frequency divider 16 is changed by a tuning operation, a phase difference due to a frequency shift is generated between the frequency divider and the reference signal, and the phase difference is eliminated. By controlling the oscillation frequency of the local oscillator 13, it is possible to oscillate according to the desired channel, and as a result, the IF signal of the desired channel is taken out from the mixer 4.

[0008]

By the way, in such a conventional configuration, an amplifier is provided between the local oscillator and the prescaler to which the oscillation signal from the local oscillator is supplied.
This amplifier amplifies the oscillation signal level from the local oscillator to the allowable level of the prescaler, and separates the prescaler from the local oscillator so that the output of the prescaler does not leak to the local oscillator side and affect the local oscillator. I am doing it. Therefore, even when the oscillation signal level from the local oscillator is sufficient and amplification by the amplifier is not required, this amplifier cannot be abolished in order to improve the separation between the prescaler and the local oscillator, which is an obstacle to cost reduction. Was there.

Further, in a tuning circuit of a PLL frequency synthesizer system using an I2Cbus used for a television receiver for Europe, a data signal of a programmable frequency divider, a clock signal of a tuning microcomputer, and others are used in the I2Cbus. Since signals for controlling the functions of are also transmitted except when tuning, if there is no amplifier between the local oscillator and the prescaler, the data signal supplied to the programmable frequency divider and its clock signal and other functions The control signal and the like leaked to the input side of the prescaler and affected the local oscillator, which sometimes caused noise in the image. The present invention has been made in view of the above circumstances, and an object thereof is to provide an oscillation output circuit capable of supplying an oscillation signal from a local oscillator to a prescaler with good isolation and at low cost. To do.

[0010]

In order to achieve the above object, the present invention provides an oscillator having a high oscillation frequency (in this case,
A high-pass filter is provided between the local oscillator) and a reduction circuit (in this case, a prescaler) that reduces the frequency of the oscillation signal supplied from the local oscillator.

The cutoff frequency of the high pass filter is set lower than the frequency of the oscillation signal output from the local oscillator and higher than the frequency of the signal output from the prescaler. Furthermore, a high-pass filter is constructed by combining a coil and a capacitor,
In this case, the ground end side of the coil is G of the prescaler IC.
It is directly connected to the ND end side.

[0012]

With this configuration, the oscillation signal from the local oscillator is supplied to the prescaler through the high-pass filter without being attenuated, and conversely, the frequency division output from the prescaler leaking due to unnecessary radiation is It will be attenuated by the high pass filter. Then, it is possible to eliminate the potential difference between the ground end of the coil and the ground end of the prescaler that form the high-pass filter, and bring the potential close to the ground potential.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The same parts as those of the conventional one are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, the local oscillator 13 and the prescaler 14 are replaced with the amplifier 15 of FIG.
A high-pass filter 22 as shown in FIG. 1 is provided between the high-pass filter 22 and the coil 23 and the capacitor 24. The cutoff frequency is set lower than the frequency of the oscillation signal output from the local oscillator 13 and higher than the frequency of the signal output from the prescaler IC 14.

In this way, the signal from the local oscillator 13 is supplied to the prescaler IC 14 through the high-pass filter 22 without being attenuated, and conversely, the frequency division from the prescaler IC 14 appearing at the input end side of the prescaler IC 14 is performed. Output is high pass filter 22
Will be attenuated at. That is, the prescaler IC14
And the local oscillator 13 are separated well, the output of the prescaler IC 14 leaks to the local oscillator 13 side, and the local oscillator 1
3 does not occur.

Further, the ground end side of the coil 23 constituting the high pass filter 22 is connected to the GN of the prescaler IC14.
Since it is connected directly to the D end side to be grounded, the common impedance in the ground pattern portion is reduced and the potential on the ground end side is made better than when connecting to the ground pattern on the substrate separately and grounding. It is possible to approach the ground potential, and the ground end side of the coil 23 and the prescaler IC1
It is possible to eliminate the potential difference between the GND terminal of No. 4 and the GND terminal. As a result, the function of the high-pass filter 22 can be sufficiently exerted, and unnecessary radiation from the prescaler IC 14 can be further suppressed.

Reference numeral 25 is a coupling coil for extracting the oscillation signal by magnetic coupling with the central conductor 26 constituting the local oscillator 13. The signal level input to the prescaler IC 14 is to strengthen the coupling of the coupling coil 25. So, you can get a sufficient level. In this case, I
Since the C-scaled prescaler is used, the ground end side of the coil forming the high-pass filter is connected to the prescaler I.
Although it is connected to the GND end of C, if the entire PLL frequency synthesizer with a built-in prescaler is integrated into an IC, the PLL frequency synthesizer IC
It will be connected to the GND end of.

[0017]

As described above, according to the oscillation output circuit of the present invention, the LC type high-pass filter is provided between the oscillator and the prescaler for reducing the frequency of the oscillation signal supplied from the oscillator. Since they are separated from each other, the circuit configuration can be simplified and the cost can be reduced. Also, since the coil that constitutes the high-pass filter is directly connected to the ground end side of the prescaler, the common impedance that occurs when grounding these ground ends is reduced, and unnecessary radiation from the prescaler is further suppressed. You can

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional example.

[Explanation of symbols]

 13 local oscillator 14 prescaler 16 programmable frequency divider 22 high-pass filter

Claims (4)

[Claims] 1. An oscillation output circuit comprising a high-pass filter between an oscillator having a high oscillation frequency and a reduction circuit for reducing the frequency of an oscillation signal supplied from the oscillator. 2. The cutoff frequency of the high-pass filter is set to be lower than the frequency of the oscillation signal output from the oscillator and higher than the frequency of the signal output from the reduction circuit. The oscillation output circuit according to Item 1. 3. The high pass filter is configured by combining a coil and a capacitor, and the ground end side of the coil is directly connected to the ground end side of the reduction circuit. Oscillation output circuit. 4. The oscillation circuit according to claim 3, wherein the reduction circuit is a prescaler formed by an integrated circuit, and a ground end side of a coil forming a high pass filter is connected to a GND end of the prescaler. Output circuit.