JPS6225543A - Frequency stabilizing system for local oscillator - Google Patents

Abstract

PURPOSE:To bring the frequency fluctuation of a local oscillator within the locking range as a demodulator by adding a part of a control voltage of a voltage control oscillator by an automatic frequency control circuit as a control voltage of the local oscillator. CONSTITUTION:After a reception modulation signal is fed to a frequency converter 2 together with a signal from the local oscillator 3, the result is inputted to a carrier recovery section 6 via an intermediate frequency amplifier 4 and a phase detector 5. The phase difference component in the output of the recovery section 6 becomes a phase synchronizing control voltage of a voltage controllers oscillator 9 via a low pass filter 8 and the frequency componentn is inputted to the oscillators 3, 9 via a frequency discriminating section 10 and a low pass filter 11 and becomes a control voltage controlling the oscillating frequency of the oscillators 3, 9. Thus, the phase control circuit including the oscillator and the automatic frequency control circuit are formed and the automatic frequency control circuit including the oscillator 3 is formed to form the duplicated automatic frequency control circuit thereby quickening the frequency locking.

Description

[Detailed description of the invention] 〔overview〕 Equipped with phase synchronization circuit and automatic frequency control circuit.

Control of the voltage controlled oscillator by this automatic frequency control circuit I
By adding a part of the 1 voltage as a control voltage to the local oscillator, the frequency fluctuation of the local oscillator is brought within the pull-in range of the demodulator, thereby stabilizing the reception operation.

[Industrial application field]

The present invention stabilizes the frequency of a local oscillator for frequency converting the received modulated signal in a receiving device for a received modulated signal such as a 4-phase PSK signal, and receives frequency-converted signals within the pull-in range of demodulation operation. This invention relates to a frequency stabilization method for a local oscillator that automatically controls the input of a modulated signal to stabilize reception operations.

[Conventional technology]

Modulation methods in microwave digital wireless communication systems include 4-phase, 8-phase PSK methods, 16-value, 64-identity Q, etc.
AM method is adopted. In such a wireless communication system, a received microwave modulated signal is converted into an intermediate frequency signal and then demodulated. FIG. 6 shows a block diagram of a conventional receiving device, in which a received modulated signal such as a microwave 4-phase PSK signal applied to an input terminal 51 is applied to a frequency converter 52 together with a local oscillation signal from a local oscillator 53. is mixed, converted into an intermediate frequency signal, and output.

This intermediate frequency signal is amplified by an intermediate frequency amplifier 54 and applied to a phase detector 55. A reference carrier signal from a voltage controlled oscillator 59 is applied to the phase detector 55, and the phase of the received modulated intermediate frequency signal is detected by this reference carrier signal, and the detected output signal is sent to the carrier regenerator 56 (CR
), this carrier wave regenerating unit 56 includes, for example, a baseband processing circuit, and detects the difference between the carrier wave phase of the intermediate frequency signal applied to the phase detector 55 and the reference carrier wave phase from the voltage controlled oscillator 59. Therefore, the phase error component is used as the control voltage of the voltage controlled oscillator 59 via the low-pass filter 58. A phase synchronization circuit is formed to synchronize the phases of the two. Further, code identification is performed by level identification of the output signal of the phase detector 55 or level identification in the carrier wave reproducing section 56, and is outputted from the output terminal 57 as a double frequency signal 7.

In order to stabilize the above-mentioned demodulation operation, it is necessary that the oscillation frequency of the local oscillator 53 for frequency conversion be stable, and for this purpose, it is possible to use a crystal oscillator. However, it is difficult for a crystal oscillator to directly oscillate microwaves. Therefore, the multiplier of the output frequency of the crystal oscillator must be made very large.

As shown in FIG. 7, it has also been proposed to stabilize the oscillation frequency of an oscillator 61 capable of directly oscillating microwaves using an automatic frequency control (AFC) circuit. That is, the output signal of the oscillator 61 is applied to the frequency discriminator 62, and the discrimination output signal corresponding to the deviation of the oscillation frequency from the center frequency is amplified by the DC amplifier 63.
It controls the

Furthermore, it is necessary that the oscillation output signal of the voltage controlled oscillation 859 is phase-synchronized with the received modulation signal input to the phase detector 55, and if the oscillation frequency of the local oscillator 53 fluctuates,
The intermediate frequency will also fluctuate, and if the frequency of the intermediate frequency signal input to the phase detector 55 fluctuates and exceeds the frequency control range of the voltage controlled oscillator 59, it will become out of synchronization and demodulation operation will no longer be possible.

Therefore, a configuration has been proposed to expand the synchronization pull-in range.For example, as shown in FIG.
It is known to provide Note that the same symbols as in FIG. 6 indicate the same parts. When the sweep circuit 64 detects an out-of-synchronization state, it superimposes a low-frequency sweep signal on the control voltage of the voltage-controlled oscillator 59 and applies it, thereby sweeping the oscillation frequency of the voltage-controlled oscillator 59. Therefore, the carrier wave reproducing section 56. When synchronization occurs due to frequency fluctuations outside the pull-in range of the phase-locked circuit including the low-pass filter 58, the sweep circuit 64 is activated, and its output signal causes the voltage-controlled oscillator 59 to start a sweep operation to perform synchronization pull-in. Become.

[Problem that the invention seeks to solve]

As mentioned above, when a crystal oscillator is used as the local oscillator 53, there is a drawback that the multiplication factor becomes very large and the cost becomes high. Further, as shown in FIG. 7, when an AFC circuit is provided, the stability of the center frequency of the frequency discriminator 62 in the AFC circuit becomes a problem, and there is a drawback that it fluctuates due to temperature fluctuations and the like. Further, as shown in FIG. 8, when a sweep circuit 64 is provided to expand the synchronization pull-in range, it is possible to prevent synchronization due to fluctuations in the oscillation frequency of the local oscillator 53, but synchronization may occur. There is no change in this, and it is not desirable for a receiving device to perform synchronization pull-in operations frequently.

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned conventional drawbacks, stabilize the frequency of a local oscillator, and enable high-speed synchronization as a demodulator circuit.

[Means for solving problems]

The local oscillator frequency stabilization method of the present invention will be explained with reference to FIG. a phase detector 103 that detects the phase of the converted received modulated signal; a voltage controlled oscillator 104;
Phase locked circuit 10 that controls this voltage controlled oscillator 104
5 and an automatic frequency control circuit 106, and the frequency and phase of the oscillation signal of the voltage controlled oscillator 104 are controlled by the phase synchronization circuit 105 and the automatic frequency control circuit 106.
111 L, voltage control 1 from automatic frequency control circuit 106
A part of the control voltage applied to the oscillator 104 is applied to the local oscillator 10
In addition to the second control voltage, the local oscillation frequency is also controlled.

[Effect]

The voltage controlled oscillator 104 is controlled by an automatic frequency control circuit 106 so as to match the frequency of the signal input to the phase detector 103, and is synchronized with the carrier phase of the signal by a phase synchronization circuit 105. As a result, high-speed synchronous pull-in is performed, and the automatic frequency control circuit 106
Since a part of the control voltage applied to the voltage controlled oscillator 104 from the voltage controlled oscillator 104 is applied as a control voltage to the local oscillator 102, the oscillation frequency of the local oscillator 102 is controlled together with the voltage controlled oscillator 104, further shortening the synchronization pull-in operation time. This makes it possible to stabilize the reception operation.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the present invention, in which 1 is an input terminal to which a received modulated signal such as a microwave 4-phase PSK signal is applied, 2 is a frequency converter, 3 is a local oscillator, and 4 is an intermediate frequency 5 is a phase detector, 6 is a carrier regenerator (C
R), 7 is a demodulated signal output terminal, 8 is a low-pass filter, 9 is a voltage controlled oscillator, 10 is a frequency discriminator, and 11 is a low-pass filter. The received modulation signal is local oscillator 3
The signal is applied to the frequency converter 2 together with the local oscillation signal from the oscillator 2, where the frequency is converted, and the resulting intermediate frequency signal is amplified by the intermediate frequency amplifier 4. The amplified output signal of the intermediate frequency amplifier 4 is applied to a phase detector 5, and phase-detected using a reference carrier signal from a voltage controlled oscillator 9.

The phase detection output signal is applied to the carrier wave regenerator 6, and the phase error component and frequency component are output from the carrier wave regenerator 6, so the phase error component is passed through the low-pass filter 8 to synchronize the phase of the voltage controlled oscillator 9. The frequency component becomes the control voltage for the control voltage, and the frequency component is changed by the frequency discriminator 10)★
The voltage is output through the low-pass filter 11 and becomes a control voltage for controlling the oscillation frequency. This control voltage is also applied to the local oscillator 3, and the oscillation frequency of the local oscillator 3 is controlled as well as the oscillation frequency of the voltage controlled oscillator 9.

Therefore, a phase synchronized circuit including the voltage controlled oscillator 9 and an automatic frequency control circuit are formed, and an automatic frequency control circuit including the local oscillator 3 is formed, thereby forming a double automatic frequency control circuit. , it becomes possible to speed up synchronization pull-in.

FIG. 3 is a block diagram of the demodulation circuit, and is for the case of receiving a four-phase PSK signal.

A four-phase PSK signal, which is a received modulation signal converted into an intermediate frequency signal by the hybrid circuit 21, is branched into two and applied to phase detectors 22 and 23. This phase detection 522.
23 corresponds to the phase detector 5 in FIG. A reference carrier signal is applied directly from the voltage controlled oscillator 34 to the phase detector 22, and a reference carrier signal phase-shifted by 90 degrees is applied to the phase detector 23 from the voltage controlled oscillator 34 via a phase shifter 35. Phase detection is performed.

This voltage controlled oscillator 34 corresponds to the voltage controlled oscillator 9 in FIG.

The phase detection output signals of the phase moxibustion devices 22 and 23 are applied to a baseband processing circuit 24 such as a Costas loop type. Oscillation frequency of voltage controlled oscillator 34 and phase detection B22
．． The difference from the frequency of the PSK signal input to the phase detector 23 is set to ω4, and the output signals of the phase detectors 22 and 23 are set to 5 inches, respectively.
(ω4 t+θ) and 7JcosCω, 1+θ), the output signal of the baseband processing circuit 24 is 5in4(
ω, t 10) and cos4 (ω, 10), and the demodulation is performed using the detector output 5in (ω 4 t + θ) and c
This is done by amplifying os (ω, t+θ) and identifying the levels.

Further, the output signal of the baseband processing circuit 24 is sent to a differentiating circuit 25.
．． 26 (d/di) and mixing circuits 27 and 28. The output signals of the differentiating circuits 25 and 26 are 4ω, respectively.
, cos4 (ω4 [10) and -4ω, 5iz4 (
The output signal of the baseband processing circuit 24 and the output signal of the differentiator circuits 25 and 26, which are ω4 [+θ], are mixed by the mixing circuit 2.
By mixing according to 7.28, each output signal ■1, v2 becomes 4ω, cos”4 (ω4 is 10)
and -4ω, sin "4 (ω4 is 10). Since the difference circuit 29 processes (V+-Vz), its output signal becomes 4ω4. In other words, the frequency difference ω, A signal multiplied by four is output from the difference circuit 29.

The output signal of this difference circuit 29 is passed through a low-pass filter 30.
It becomes a control voltage for the voltage controlled oscillator 34 via the amplifier 31. Therefore, when the difference ω between the signal frequency and the oscillation frequency of the voltage controlled oscillator 34 is detected, the voltage controlled oscillator 34 is controlled so that the difference ωd becomes zero, and the automatic frequency word ?
11 (AFC) circuit is formed. That is, the voltage controlled oscillator 34 is controlled by the relationship between the frequency difference ω and the control voltage shown in FIG. Also amplifier 3
The control voltage of the output of 1 is applied as the control voltage of the local oscillator 3 shown in FIG.

Also, either one of the output signals of the baseband processing circuit 24,
That is, 5in4 (ω, t+θ) and cos4 (ω, [+
θ) is amplified by an amplifier 32 and passed through a low-pass filter 33 to a voltage-controlled oscillator 34.
becomes the control voltage. This control voltage has a value corresponding to four times the difference θ between the signal phase and the output signal phase of the voltage controlled oscillator 34, and since the voltage controlled oscillator 34 is controlled so that this phase difference θ becomes zero, the phase A synchronous circuit will be formed.

Therefore, the output signal of the baseband processing circuit 24 is
This corresponds to the output signal of the carrier wave regenerator 6 which is applied to the low-pass filter 8 and the frequency discriminator 10 in the figure, the low-pass filter 33 corresponds to the low-pass filter 8 in FIG. 2, and the differentiating circuits 25, 26, Mixing circuit 27.28,
The configuration consisting of the difference circuit 29 corresponds to the function of the frequency discriminator 10 in FIG. 2, and the low-pass filter 30 corresponds to the low-pass filter 11 in FIG.

The voltage controlled oscillator 34 is, for example, as shown in FIG.
A variable capacitance diode 41 is connected in parallel to the oscillation circuit section 44 such as a transistor. Capacitor 42. Coil 43 is connected,
It has a configuration in which the oscillation frequency changes in response to the voltage applied to the variable capacitance diode 41. This voltage control generator J! The control voltage (31) applied to the amplifier 31 in FIG. 3 is the control voltage for frequency control, and the control voltage (33) is the output signal of the amplifier 31 in FIG. 33, that is, a control voltage for phase control.Thereby, the control voltage (31) has a polarity corresponding to the positive or negative of the frequency difference ω4,
Further, the control voltage (33) has a polarity corresponding to the positive or negative phase difference, and is applied to the variable capacitance diode 41 in a superimposed manner.

The local oscillator 3 is composed of elements such as a bipolar transistor for the microwave band, a GaAs FET, a Gunn diode, and an imbat diode, and the oscillation frequency is controlled by changing parameters by controlling the bias voltage, changing the capacitance of the varactor, etc. Therefore, the local oscillation frequency can be controlled by applying a control voltage from an automatic frequency control circuit.

〔Effect of the invention〕

As explained above, the present invention provides a phase synchronized circuit consisting of a local oscillator 3, a phase detector 5, a voltage controlled oscillator 9, a low pass filter 8 for controlling the voltage controlled oscillator 9, etc. Equipped with an automatic frequency control circuit consisting of a low-pass filter 11 etc. for controlling the oscillator 9,
A part of the control voltage from the automatic frequency control circuit is added as a control voltage to the local oscillator 3. The oscillation frequency of the voltage controlled oscillator 9 is controlled by the control voltage from the automatic frequency control circuit to perform synchronization pull-in, and at the same time, the local Since the oscillation frequency of the oscillator 3 is controlled, synchronization can be achieved in a short time. Furthermore, when the oscillation frequency of the local oscillator 3 fluctuates, the automatic frequency control circuit controls the voltage controlled oscillator 9 as well as the local oscillator 3, thereby stabilizing the operation as a demodulation circuit.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the principle of the present invention, Fig. 2 is a block diagram of an embodiment of the invention, Fig. 3 is a block diagram of a demodulation circuit, Fig. 4 is a characteristic curve diagram of frequency difference and control voltage, Figure 5 is an example of a voltage controlled oscillator, Figure 6 is a block diagram of a conventional receiver, Figure 7 is a block diagram of an automatic frequency control circuit, and Figure 8 is a block diagram of an automatic frequency control circuit.
The figure is a block diagram of a conventional example provided with a sweep circuit. 1 is the input terminal, 2,101 is the frequency converter, 3.102
is a local oscillator, 4 is an intermediate frequency amplifier, 5.22.23.
103 is a phase detector, 6 is a carrier wave regeneration unit, 7 is an output terminal, 8.11 is a low-pass filter, 9.34.104 is a voltage-controlled oscillator, 10 is a frequency discrimination unit, 11.30 is a low-pass filter, and 21 is a hybrid circuit, 24 is a baseband processing circuit, 25.26 is a differentiation circuit, 27:28 is a mixing circuit, 29 is a difference circuit, 105 is a phase synchronization circuit, 10
6 is an automatic frequency control circuit.

Claims (1)

[Claims] A local oscillator (102) that outputs a local oscillation signal for converting the frequency of the received modulated signal, a phase detector (103) that phase-detects the frequency-converted received modulated signal, and a reference carrier signal to the phase detector. A voltage controlled oscillator (1
04), a phase locked circuit (105) and an automatic frequency control circuit (106) for controlling the voltage controlled oscillator, and a part of the control voltage of the voltage controlled oscillator by the automatic frequency control circuit is transmitted to the local area. A local oscillator frequency stabilization method characterized by applying it as an oscillator control voltage.