JPS61287327A - Phase locked oscillator - Google Patents

Abstract

PURPOSE:To suppress minute spurious radiation and to prevent adverse effect onto a high frequency signal system by providing a filter circuit passing through an output signal of a voltage controlled oscillator and interrupting an undesired signal to the voltage controlled oscillator from a phase comparator to a path feeding the oscillated output of the voltage controlled oscillator to the phase comparator. CONSTITUTION:A band pass filter 2' passes a signal having a frequency within the control range of a voltage controlled oscillator (VCO) 1 and stops the passing of a signal having a higher and a lower frequency than the range. Since the low order harmonics being a problem as a conventional spurious signal have a sufficiently lower frequency than the range of the oscillation frequency of the VCO 1, they are stopped by the said band pass filter 2' and hardly propagated toward the VCO 1 from the phase comparator 3. The said dielectric resonator 2' has a passing characteristic along the resonance characteristic curve, the Q is increased to make the slope of the curve steep and the attenuation of low frequencies is increased, then the spurious signal of low harmonics is suppressed remarkably by using the said resonator using the center frequency of the oscillated frequency within the control range of the VCO 1 as the resonance frequency as the filter circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvement of spurious characteristics from a phase comparator of a phase synchronized oscillator used as a local oscillator of a receiving device in a microwave band to a voltage controlled oscillator.

(Prior Art) A phase synchronized oscillator whose phase is synchronized to a highly stable reference signal source for the purpose of stabilizing the oscillation frequency is well known.

Figure 4 shows a conventional phase-locked oscillator. In Figure 4, 1 is a voltage controlled oscillator.
dOscillator (hereinafter referred to as VCO), and a part of the zero oscillation output oscillating at the oscillation frequency f is input to the phase comparator 3 via the isolator 6.

The phase comparator 3 detects the phase difference with the reference signal frequency fX, and the loop filter (phase difference/voltage converter) 4 applies a voltage according to the phase difference to the modulation element of the VCo. This controls the frequency of the VCO and closes the phase-locked loop at the frequency. is phase-locked to a frequency that is an integral multiple of fX. In this way, an oscillation signal with high frequency stability is obtained.

(Problem to be Solved by the Invention) However, in the above conventional phase-locked oscillator, the low-order harmonics of the frequency reference signal enter from the phase comparator 3 toward the VCOI, and the spurious signal is directly transmitted to the output terminal of the voltage-controlled oscillator. The problem is that it appears as This means that the frequency characteristic of the isolation run of isolator 6 is the frequency f
For frequency f
This is because the isolation function is low for 4fX, etc.).

If such a phase-locked oscillator is used as a local oscillator in a low-noise receiver, the received signal level will be very low, and this spurious will have an adverse effect on the high-frequency signal system.

The purpose of the present invention is to provide a phase-locked oscillator that suppresses even such minute spurious (means for solving the problem). It has the following configuration.

That is, a voltage controlled oscillator, a phase comparator that detects the phase difference between the oscillation output of the voltage controlled oscillator and a reference frequency signal,
In a phase synchronized oscillator whose oscillation frequency is stabilized by a phase difference/voltage converter that converts the phase difference signal into a frequency control voltage according to the phase difference and sends it to a voltage controlled oscillator,
In the path that sends the oscillation output of the voltage controlled oscillator to the phase comparator,
This is a phase synchronized oscillator that has a filter circuit that allows the output signal of the voltage controlled oscillator to pass through while blocking unnecessary signals from the phase comparator to the voltage controlled oscillator.

FIG. 1 is a block diagram showing the configuration of the present invention. 1 is a voltage controlled oscillator (vC○), 2 is a filter circuit, 3 is a phase comparator, 4 is a phase difference/voltage converter (loop filter), f
x is the reference frequency and f is the oscillation frequency.

(Operation) The operation of the phase synchronized oscillator of the present invention will be explained below based on the drawings. Note that a description of operations similar to those of a conventional phase-locked oscillator will be omitted.

The difference between the phase-locked oscillator of the present invention and the conventional one is that a filter circuit 2 is used in the part where an isolator 6 was conventionally used.The filter circuit 2 used in the present invention compares the phase of the oscillation output of the VCOI. This circuit has the effect of blocking and suppressing unnecessary signals such as low-order harmonics of the fundamental frequency signal passing from the phase comparator 3 toward the VCOI.

Therefore, the phase synchronization effect is performed in the same way as in a conventional oscillator, but the level of unnecessary signals such as low-order harmonics of the fundamental frequency signal output from the phase comparator 3 and input to the vcoi is significantly suppressed to a low level. becomes.

Therefore, the level of these unnecessary signals output as spurious signals from the output terminal of the VCOI is also significantly lowered, and even when used as a local oscillator of a low-level receiving circuit,
There will be no negative effects like before.

(Example) Examples of the phase-locked oscillator of the present invention will be described below based on the drawings.

FIG. 2 shows a case where a bandpass filter or a dielectric resonator is used as the filtering circuit.

A bandpass filter is a filter that passes signals with frequencies within the control range of the VCOI, but blocks and suppresses signals with frequencies higher and lower than that range. Since the low-order harmonics have a frequency sufficiently lower than the oscillation frequency range of the VCOL, they are blocked and suppressed by this bandpass filter, making it difficult for them to propagate from the phase comparator 3 to the VCOI. It has a pass characteristic that follows the resonance characteristic curve, and by increasing the Q, the slope of the curve becomes steeper, and the attenuation in the low range can be increased, so the center frequency of the oscillation frequency in the VCOI control range can be set to the resonance frequency. By using a dielectric resonator as a filter circuit, spurious signals of low-order harmonics can be significantly suppressed.

FIG. 3 shows an example in which a cascaded circuit of an isolator 6 and a high-pass filter 7 is used as a filter circuit.

The high-pass filter is a low-pass filter that passes signals at the oscillation frequency of the VCO and blocks signals at lower frequencies. This is an attempt to compensate for this point using a low-pass filter.

The degree of improvement in spurious suppression in these examples is as follows. The frequency is fa = 2.3GHz, fx”
This is a value actually measured as 60MH2.

Also, the spurious signal level is determined by the required signal (Desir).
e signal) and spurious signals, that is, unnecessary signals (Unde
The ratio D/U to the s i re flaw signal is expressed in dB.

In the conventional configuration shown in FIG. 4, the eighth harmonic was output at 70 dB. On the other hand, in the embodiment shown in Fig. 2, when a bandpass filter is used, it is 100 dB, and when a dielectric resonator is used, it is 110 dB.
The above data were obtained. In the example shown in Figure 3, 100d
D/U of B was obtained. As a result, the degree of improvement in spurious suppression of the phase synchronized oscillator of the present invention is 30 dll to 40 dB. Note that the fx harmonics generated from the phase comparator may not be one wave but several waves, but in that case, by increasing the number of filter stages or raising the Q of the dielectric resonator, the spurious waves of several waves can be suppressed. can be suppressed.

(Effects of the Invention) Since the phase synchronized oscillator of the present invention has the configuration and operation described above, it can suppress spurious in the low frequency region with a simple configuration, and can be used in local oscillators such as microwave low noise receivers. It has an extremely large practical effect when used as a.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention, FIGS. 2 and 3 are block diagrams showing the configuration of an embodiment of the present invention, and FIG.
The figure is a block diagram showing the configuration of a conventional phase-locked oscillator. 1... Voltage controlled oscillator (VCO), 2...
... Filter two-wave circuit, 2'...Band pass filter or dielectric resonator, 3... Phase comparator,
4... Phase difference/voltage converter (loop filter)
, 6...Isolator, 7...High-pass filter agent Patent attorney Yoshihiro Yawata A. Mitsuaki's (Fig. 1) Mitsuaki Moto's first tip , Mizowei Diagram $ 2 Diagram

Claims (3)

[Claims] (1) a voltage controlled oscillator; a phase comparator that detects a phase difference between the oscillation output of the voltage controlled oscillator and a reference frequency signal;
In a phase synchronized oscillator whose oscillation frequency is stabilized by a phase difference/voltage converter that converts the phase difference signal into a frequency control voltage according to the phase difference and sends it to a voltage controlled oscillator,
In the path that sends the oscillation output of the voltage controlled oscillator to the phase comparator,
A phase-locked oscillator characterized by having a filter circuit that passes an output signal of the voltage-controlled oscillator while blocking unnecessary signals from the phase comparator to the voltage-controlled oscillator. (2) The phase synchronized oscillator according to claim (1), wherein the filtering circuit is a bandpass filter or a dielectric resonator. (3) The phase synchronized oscillator according to claim (1), wherein the filter circuit comprises a cascaded circuit of an isolator and a high-pass filter.