JPS6334661B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic frequency control device used in the SHF or UHF band.

Conventionally, the oscillation frequency in ultra-high frequency bands such as the SHF band is determined by forming harmonics of the reference frequency using a multiplier, and frequency-mixing this with the oscillation output of a voltage-controlled oscillator (hereinafter referred to as VCO) to be stabilized. After converting to an intermediate frequency, frequency discrimination is performed to extract an error voltage, which is used to control the oscillation frequency of the VCO, thereby stabilizing the voltage.

However, in such a configuration, since the band of the harmonic signal to be frequency-mixed with the VCO output is controlled by the band of the multiplier, the band of the automatic frequency control device is limited. To avoid this, a multistage combination of a multiplier and a bandpass filter (hereinafter referred to as BPF) is used.
The entire device therefore has a complex configuration. on the other hand,
The harmonic signal that is the output of the multiplier may leak into the VCO output through the down converter and be output, resulting in low reliability.

An object of the present invention is to solve these problems and provide an automatic frequency control device that can be used over a wide band and has a simple configuration.

According to the present invention, a voltage controlled oscillator that generates an oscillation output with a frequency v that changes in response to a control voltage; a high frequency signal source that generates a high frequency signal with a reference frequency x;
In order to generate a pulse train containing harmonic components nx of x, a multiplier diode is connected; a first circuit including a grounded transformer; a pair of series detection diodes coupled in parallel to the multiplier diode, each coupling point being grounded via a series circuit of a resistor and a capacitor; Input the frequency v at the connection point between the series detection diodes,
A second circuit that outputs the difference component between the harmonic component nx and the frequency v from the connection point between the resistor and the capacitor in the series circuit.
A frequency discriminator for detecting the frequency fluctuation of the difference component; and means for supplying the output of the frequency discriminator as a control voltage to a voltage-controlled oscillator to stabilize the frequency v. An automatic frequency control device is obtained.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 shows a block diagram of an embodiment of the invention.
First, the reference frequency supplied from the crystal oscillator 11
The x signal is fed to a pulse generator 12 to form a pulse signal with a repetition frequency x. This pulse signal includes a harmonic component nx of frequency x. This pulse signal is supplied to the switching circuit 13 to switch the output signal (frequency v) of the VCO 10. Therefore, this output waveform is an intermittent signal of frequency v at repetition frequency x. This output signal includes a difference frequency component |nx−v| between the frequency _V and the high frequency component nx. The harmonic nx is the frequency closest to the frequency v, and the frequency component |nx−v| is 1/of the frequency x.
It is appropriate for the design to select 3 or less. This difference frequency component |nx-v| is amplified by an amplifier 14 and supplied to a frequency discriminator 15. This frequency discriminator 15 detects the frequency variation of the difference frequency component |nx-v| with reference to the reference frequency _p of another crystal oscillator 16.

This frequency discriminator 15 is a digital frequency discriminator as described in Japanese Patent Application No. 52-27571, and is a period during which the phase difference between two input waves corresponds to 0 to +180 degrees and 0 to -180 degrees. , a digital phase detector (for example, μPC1008C manufactured by NEC) that outputs a rectangular wave with a constant peak value, and two low-pass filters that block the input wave and its harmonics from each output. Two high-pass filters that create slopes in the frequency discrimination characteristics of the respective outputs of these low-pass filters, and a means for rectifying the two outputs of these high-pass filters to extract a voltage difference between them. configured. Since this frequency discriminator is composed of a digital circuit, it operates stably without responding to unnecessary mixed waves, and is therefore suitable for a circuit including unnecessary mixed waves as in this embodiment.

The differential voltage from this frequency discriminator is VCO10
It becomes a control voltage that is supplied to the oscillator and controls its oscillation frequency. The output signal of this VCO 10 is fed back to the switching circuit 13 to configure an automatic frequency control loop, and the frequency |nx-v| is set to the reference frequency o.
The output frequency v of the VCO is stabilized.

FIG. 2 is a specific circuit diagram of the pulse generator 12 and switching circuit 13 shown in FIG. 1.

The pulse generator 12 includes a multiplier diode D1,
It consists of a transformer T1 whose input end 20 is connected to a high frequency source (crystal oscillator) 11, whose output end is connected in parallel to a multiplier diode D1, and whose parallel connection points are grounded via resistors R1 and R2, respectively. The switching circuit 13 is connected in parallel to the multiplier diode D1, and the coupling point is connected to a pair of series detection diodes D2 and D3 which are grounded through a series circuit of a resistor R6 and a capacitor C4, and a resistor R5 and a capacitor C3, respectively. It is configured. Pulse generator 12 and switching circuit 1
3 are resistors R3, R4 and capacitors C1, C
2. The frequency v is inputted from the input terminal 21 to the connection point between the series diodes D2 and D3 through the resistor R7, and the frequency v is inputted from the resistor R8 connected in series between the resistor R6 and the capacitor C4.
harmonic component nx and frequency from output end 22 via
Outputs the difference component with v. The frequency relationship in this example is that frequency x is 100MHz (i.e., repetition period 10ns), frequency _p is 20MHz, and frequency v is
7020MHz, multiplication number n is 70. First, when a signal with a reference frequency (x) of 100 MHz is supplied to the input terminal 20, the pulse generator converts the transformer T ₁ and step recovery diode D ₁ (for example, NEC
SV24B) outputs a positive pulse to the cathode side of this diode D ₁ and outputs a negative pulse to the anode side. In this specific example, pulses with a repetition period of 10 ns and a pulse width of 1 to 2 ns were observed.

The positive pulse is applied to the anode side of the diode D ₃ (for example, NEC ISS12) of the switching circuit 13.
Negative pulses are simultaneously supplied to the cathode side of diode D ₂ , and these diodes D ₂ and D ₃ are ON only while this pulse is being supplied. Therefore, the output signal (7GHz) of the VCO supplied from the input terminal 21 is the output signal of these diodes _D2 and _D3 .
While ON, it is output to the connection point between resistor R ₆ and bypass capacitor C ₄ . This output changes from 1 to 1 with a period of 10 ^ns .
It is a pulsed waveform containing a 7 ^GHz signal with a width of 2 ^ns , and naturally contains a difference frequency component |nx−v|, i.e., 20 ^MHz , and this 20 MHz signal, which is a low frequency component, is bypassed with capacitor C ₄ . The signal is outputted to the output terminal 22 without any interference. This 20 ^MHz component is amplified by the amplifier 14 and is then set to the reference frequency of the crystal oscillator 16.
Frequency discrimination is performed based on 20 ^MHz .

Note that the multiplier n of the pulse generator is necessarily n = when the frequency variable range in which the VCO operates is narrow (for example, in the above example, v = 7 ^G Hz ± 50 ^M Hz).
70, but when no control voltage is applied
Even if the VCO oscillation frequency can be set to 7 ^GHz , n =
It can be determined as 70.

The pulse generator and switching circuit that constitute this invention have a wide band because they do not have any band-limiting elements, and even when changing the frequency v of the VCO,
It can be used at any frequency by simply changing the frequency of the crystal oscillator 11. Furthermore, the multiplier circuit of the present invention does not require a multi-stage BPF, which simplifies the circuit configuration. Furthermore, since the switching circuit is configured to simultaneously supply positive and negative pulses to the anode and cathode sides of the series-connected detection diodes, the operating level of the frequency component nx near the frequency v is lower than that of the conventional one. Since it can operate at a lower level than the mixer operating level, the frequency component nx leaking to the output side of the VCO can be reduced, and a frequency output with less spurious can be obtained.

As explained above, the automatic frequency control device of the present invention is effective for frequency stabilization in the ultra-high frequency band above the SHF band by widening the frequency band and simplifying the circuit configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a partial circuit diagram of FIG. In the figure, 10...VCO, 11, 16...Crystal oscillator,
12... Pulse generator, 13... Switching circuit, 14... Intermediate frequency amplifier, 15... Digital frequency discriminator, 20, 21... Input end, 22...
...is the output end.

Claims (1)

[Claims] 1. A voltage-controlled oscillator that produces an oscillation output with a frequency v that changes in response to a control voltage; a reference frequency x
a high-frequency signal source that generates a high-frequency signal; a multiplier diode for generating a pulse train including a harmonic component nx of the reference frequency x in response to the high-frequency signal; an input end connected to the high-frequency source; a first circuit including a transformer whose output end is connected in parallel to the multiplier diode, and each parallel connection point is grounded via a resistor; A pair of series detection diodes are grounded through a series circuit of a resistor and a capacitor, and the frequency v is connected to the connection point between the series detection diodes.
and a second circuit that outputs a difference component between the harmonic component nx and the frequency v from a connection point between the resistor and the capacitor of the series circuit; a frequency discriminator that detects frequency fluctuations of this difference component; and; means for supplying the output of the frequency discriminator to the voltage controlled oscillator as the control voltage;
An automatic frequency control device characterized by stabilizing v.