JPH0339962Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field) This invention relates to a tracking voltage generator in a frequency synthesizer.

(Prior art and its problems) An embodiment of a conventional frequency synthesizer that generates a tracking voltage is shown in FIG. 1 is a frequency synthesizer, which includes a voltage controlled oscillator 2 that varies the oscillation frequency using a control voltage, a frequency divider 3 that divides the output of the voltage controlled oscillator 2, and a phase that compares the output of the frequency divider 3 with the phase of the reference oscillator 5. It is composed of a comparator 4 and a low-pass filter 6, and the output of the phase comparator 4 is passed through the low-pass filter 6 to the voltage controlled oscillator 2.
will be returned to. 7 is the output of the voltage controlled oscillator 2, and 8 is the control voltage of the voltage controlled oscillator 2, which is used as the tracking voltage. This method has the disadvantage that the tracking range is the range of the control voltage of the voltage controlled oscillator 2, making it difficult to widen the band. That is, in order to widen the band, the modulation sensitivity of the voltage controlled oscillator 2 must be increased, and if the modulation sensitivity is increased, there is a problem in that C/N, S/N characteristics, etc. deteriorate.

(Purpose) In order to eliminate these drawbacks, this invention switches the oscillation frequency band of the voltage controlled oscillator to multiple,
The plurality of discontinuous control voltages are passed through a DC amplifier to be converted into one continuous DC voltage, and this DC voltage is used as a tracking voltage to widen the tracking range. Another purpose of this invention is to switch the oscillation frequency band of the voltage controlled oscillator into multiple bands to widen the band without increasing the modulation sensitivity, and to obtain a frequency synthesizer with good C/N and S/N characteristics over a wide band. be.

(Example) An example of this invention will be described below with reference to FIG. 1 is a frequency synthesizer, which includes a voltage-controlled oscillator 2 whose oscillation frequency can be varied by a control voltage and whose oscillation frequency band can be switched;
a frequency divider 3 that divides the output of the frequency divider 3; a phase comparator 4 that compares the output of the frequency divider 3 with the phase of the reference oscillator 5;
The output of the phase comparator 4 is fed back to the voltage controlled oscillator 2 via the low pass filter 6. 7 is the output of the voltage controlled oscillator 2, and 8 is a tracking voltage, which is produced by passing the control voltage of the voltage controlled oscillator 2 through a DC amplifier 9 constituted by an operational amplifier 10 and resistors 11 and 12 that determine the gain. 13 is a switching signal for switching the reference voltage of the voltage controlled oscillator 2 and the preamplifier 10.
The DC amplifier 9 is a circuit that converts the discontinuous control voltage obtained by switching the oscillation frequency band of the voltage controlled oscillator 2 shown in FIG. 3 into one continuous DC voltage as shown in FIG. It is. The broken line in FIG. 4 shows the voltage before the switching signal 13 is applied to the operational amplifier 10. This makes it possible to widen the tracking range, and also eliminates the need to increase the modulation sensitivity of the voltage controlled oscillator, resulting in C/N and S/N
A frequency synthesizer with good characteristics can be obtained.

(Effects) The frequency synthesizer according to this invention can widen the tracking range without increasing the modulation sensitivity of the voltage controlled oscillator, and also has C/N, S/
A frequency synthesizer with good N characteristics can be realized.

[Brief explanation of drawings]

Figure 1 is a block diagram of a frequency synthesizer according to an embodiment of the present invention, Figure 2 is a block diagram of a conventional frequency synthesizer, Figure 3 is oscillation frequency vs. control voltage characteristics, and Figure 4 is oscillation frequency vs. tracking voltage characteristics. It is. 1: Frequency synthesizer, 2: Voltage controlled oscillator, 3: Frequency divider, 4: Phase comparator, 5: Reference oscillator, 6: Low pass filter, 7: Oscillation output, 8:
tracking voltage, 9: DC amplifier, 10: operational amplifier, 11, 12: resistor, 13: switching signal.

Claims (1)

[Scope of utility model registration request] In a frequency synthesizer that has a voltage controlled oscillator that can switch between a plurality of oscillation frequency bands and generates a tracking voltage using the control voltage of the voltage controlled oscillator, the frequency synthesizer has a method for switching the oscillation frequency band of the voltage controlled oscillator. A DC amplifier controlled by the same switching signal as the signal is added, and the discontinuous control voltage of the voltage controlled oscillator caused by switching the oscillation frequency band is converted into a continuous DC voltage by passing it through the DC amplifier. A tracking voltage generator characterized in that the tracking voltage is a direct current voltage.