JPS5827404A - Oscillating circuit - Google Patents

Abstract

PURPOSE:To obtain an oscillation circuit with good stability and a wide variety of frequency varying range, by generating a frequency of sum of input frequencies at a mixer and generating a frequency of the difference of input frequencies at another mixer, through the provision of the mixers before and after a delay line. CONSTITUTION:A frequency mixer 2 mixes an output of a varible frequency oscillators in which the oscillatin frequency omega0 is changed with a control voltage Vc with an output omega of an amplifier 1 and a signal in frequency (omega-omega0) is selected at a band-pass filter 3 for the amplitude characteristics. The output of the filter 3 is mixed with the output of the oscillator 6 at a mixer 5 via a delay line 4, and the component in frequency omega is again picked up at a band-pass filter 7 and the component is applied to the input of the amplifier 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oscillation circuit using a delay line such as a surface acoustic wave device.

Conventionally, this type of oscillation circuit is configured as shown in FIG. 1, for example, where 1 is an amplifier with a gain of G and a phase shift amount of π, 2 is a delay line with a delay time Δt, and 3 is a band-pass filter. , 4 is a variable phase shifter, whose phase shift amount Φ is the external voltage V. Assuming that it can be controlled by , the oscillation conditions determined by the loop-tour phase shift amount and the loop-tour gain are as follows.

π+ω△t+Φ(Vc) =:2 nπ...
・・・・・・0)GXF←)≧1 ・・・・・・・・・
・・・・・・・・・・・・・・・(2) Generally, there are many frequencies that satisfy the phase condition, but in order to prevent oscillation at frequencies other than the intended one, a bandpass filter 3 is required. It is necessary to narrow the band so that the gain condition is not satisfied.

In order to increase the short-term stability of the oscillator, it is necessary to increase Δt, but when Δt is increased, frequencies that satisfy the phase condition occur every 1-(Hz).

Δt Therefore, the bandwidth of the band-pass p-wave generator cannot exceed 1 (Hz), and the oscillation frequency range of the oscillator also exceeds Σ1
ω2) cannot be exceeded.

The present invention aims to eliminate such drawbacks and provide an oscillator with a high C/N (carrier-to-noise ratio) over a wide variable frequency range.

Hereinafter, one embodiment of a certain invention will be described in detail. FIG. 2 shows an embodiment of the present invention, in which 1 is an amplifier;
It is assumed that the gain in the oscillation frequency band is 01 and the phase shift amount is π (radian). 2 is a frequency mixer, which has an oscillation frequency ω at a control voltage VC. The output of the variable frequency oscillator 6, which changes, and the output of the amplifier 1 (frequency ω) are mixed, and the resulting signal with a frequency of (ω-ω) has an amplitude characteristic F2(ω)
The selection is made using the bandpass filter 3. Bandpass filter 3
The output passes through a delay line 4 with a delay time Δt, is mixed with the output of a variable frequency oscillator 6 in a mixer 5, is passed through a bandpass filter, and a component of frequency ω is extracted again, and this is added to the input of the amplifier 1. For ease of explanation, bandpass filter 3
Assuming that the delay time of is zero and there is no passing loss in mixers 2 and 6 and delay line 4, the loop configured in this way has GxF(ω-ω.)≧1.・・・
... (3) π+(ω-ω.)×Δt = 2 nπ
...... Oscillates at a frequency ω that satisfies (4). If the bandwidth of the bandpass filter 3 is sufficiently small, satisfying (4) (ω-ω.) is limited to − frequencies, so by changing the control voltage v0 to vc+△■o, the variable frequency oscillator can be oscillated. The frequency is ω. +△ω. When the variable frequency oscillation frequency ω0 is changed, ω changes to ω+△ω, and the relationship becomes Δω1△ω0 from equation (4). When the variable frequency oscillation frequency ω0 is changed, the oscillation frequency ω of the loop also changes by the same amount. .

In this way, the output of mixer 2 is ω. Since it is possible to maintain a constant frequency regardless of changes in The overall oscillation frequency can be varied regardless of the That is, even if Δt is made sufficiently large in order to improve the short-term stability of the oscillation frequency generator, the oscillation frequency can be varied without being limited by this.

In the above explanation, ω10ω in mixer 2. frequency,
Mixer 3 (ω+ω.)−ω. Even if you create a frequency = ω, ω = -△ω. It is exactly the same except that.

Also, Figure 2! It can be seen that the portion 8 surrounded by the dotted line constitutes a variable phase shifter.

Next, FIG. 3 shows an example of a synthesizer to which the oscillation circuit shown in FIG. 2 is applied. Here, the amplifier 1, mixer 2, bandpass filter 3, delay line 4, mixer 6, variable frequency oscillator 6, and bandpass filter 7 constitute an oscillation circuit shown in FIG. 2, which oscillates at a frequency ω. After branching the output of the amplifier 1 and dividing the frequency by N by the frequency divider 9, the frequency phase detector 10 performs frequency phase detection with the output of the highly stable crystal oscillator 11 with a frequency of ω, and detects the phase error through the loop filter 12. The voltage is fed back to the frequency control terminal of the variable frequency oscillator 6.

By doing this, the oscillation frequency ω is fixed to N×ω, and as the division ratio of the frequency divider 9 is changed by 1, ω can be changed by ω. It goes without saying that the bandpass filter 3 and the delay line 4 can be constructed using one surface acoustic wave element.

As described above, according to the present invention, the delay time of the delay line can be selected to be long without being controlled by the frequency variable range of the oscillator, so that the variable oscillator has a wide frequency variable range and excellent short-term stability. can be constructed, and its industrial value is large.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional delay line oscillator, and FIG. 2 is a block diagram of a variable frequency delay line oscillator according to an embodiment of the present invention.
FIG. 3 is a block diagram of a frequency synthesizer to which the variable frequency delay line oscillator of the present invention is applied. 1... Multiplier, 2... Mixer, 3...
...Bandpass filter, 4...Delay line, 6
...Mixer, 7...Band pass filter, 6...Variable frequency oscillator.

Claims (1)

[Claims] A mixer that uses the output of a common variable frequency oscillator as a local signal is installed before and after the delay line with a limited pass band, and one mixer generates a frequency that is the sum (or difference) of the input frequency, and the other An oscillation circuit configured to generate a frequency that is the difference (or sum) of the input frequency using a mixer.