JPS61202501A - Voltage controlled oscillator for pll - Google Patents

Abstract

PURPOSE:To operate stably a phase locked loop by impressing a frequency control voltage to other end of a varactor diode via a high pass filter, a phase adjusting circuit and an amplitude adjusting circuit connected to the filter. CONSTITUTION:The cut-off frequency of the high-pass filter 13 is selected to a frequency lower than a comparison frequency leaked as a frequency control voltage from a phase comparator, and phase and amplitude adjusting circuits 14, 15 are used to adjust the amplitude difference and phase difference of both a DC amplifier 12 and an amplitude adjusting circuit 15 zero when the frequency control voltagehas the same frequency as the comparison frequency. In this case, the cut-off frequency is adjusted so that the adjustment of phase and amplitude is less. In adjusting each section in this way, since the signal of a comparison frequency component included in the frequency control voltage is impressed across the varactor diode 17 in the same amplitude and phase, the capacitance of the varactor diode 17 is unchanged and the output of the VCO does not respond to the signal of comparison frequency component included in the frequency control voltage.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a voltage controlled oscillator for PLL (phase locked loop) (
(hereinafter referred to as vCO).

[Conventional technology]

Conventionally, in a VCO using a variable capacity violet diode in a resonant circuit, a frequency control voltage is applied to one end of the variable capacity violet diode, and the other end is grounded or a DC voltage is applied. In response to the rounding and high frequency components of the frequency control voltage, the VC
The problem of fluctuating output circumferential ridges frequently occurred.

[Problem that the invention seeks to solve]

This conventional vCO also responded to high frequency components of the frequency control voltage, so the phase comparator output κ does not vary depending on the included comparison frequency components, and the phase comparator output passes through a low frequency range. VCO through filter
is being entered.

Therefore, in order to sufficiently attenuate the comparison frequency component inputted by this manual frequency control of vCO voltage Kt, it is necessary to make the cutoff characteristic of the low-pass filter steep. However, when the cutoff frequency is lowered, the PLL loose band becomes narrower. There is also a drawback that if the shielding ffr characteristic is made steep, the phase of the PLL loop rotates, making the loop unstable.

SUMMARY OF THE INVENTION An object of the present invention is to provide a PLL VCO that eliminates such drawbacks, eliminates output frequency fluctuations due to high frequency components, and enables stable operation of a PLL loop.

[Means for solving problems]

The present invention provides a voltage controlled oscillator for PLL in which a variable valley type diode is used in a resonant circuit and a control voltage is applied to -1 of the variable capacitance diode to control the oscillation frequency. The end is characterized by a high-pass filter and a wire to which the frequency control voltage is applied via a phase adjustment circuit and an amplitude adjustment circuit connecting the output of this filter.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention. In the figure, 11
is a frequency control voltage input terminal, 12 is a DC amplifier, 13 is a high-pass filter, 14 is a phase investigation circuit, 15 is an amplitude adjustment circuit, 17 is a variable capacitance diode, 16.18 is a DC cut capacitor, 19 is a An inductor, 22 a transistor, 19.21 a feedback capacitor, 20 a DC cut capacitor, and 22 a CO output terminal. The four components 16 to 22 constitute a collector-grounded Colpitts ejector.

Here, the ratio between the cutoff frequency d' of the high-pass filter 13 and the frequency control 1gl voltage from the phase comparator is 411! At a frequency lower than the frequency 9, and by using the phase and amplitude adjustment circuits 14 and 15, when the voltage is at the same frequency as the comparison frequency, the DC amplifier 12 and the smooth tuning circuit are adjusted.
r15 so that the imaging difference and phase difference of both outputs become 0 w4
! ! do. At this time, the cut-off frequency of the high-pass filter is adjusted so that the phase and amplitude tuning is minimal.

The above VRK parts are fJ! 4, the signal of the comparison frequency component included in the frequency control voltage is applied to both ends of the variable cap diode 17 with the same amplitude and the same phase, so the capacitance of each variable cap diode 17 does not change. Therefore vC
The output of O does not respond to the comparison frequency component signal contained in the frequency control voltage. Also, when a frequency component higher than the high-pass filter cutoff frequency is added to the frequency control voltage,
Signals having substantially the same phase and the same amplitude are applied to both ends of the variable capacitance diode 170, and the fluctuation in the output of vCO is reduced. vice versa,
When a frequency component lower than the high-pass filter cutoff frequency is added to the frequency control voltage, the 1δ signal with a larger amplitude is applied to the cathode side of the variable valley diode 17 than the anode side.
The output frequency of vCO responds to that frequency word @voltage.

As described above, in this embodiment, when the cutoff frequency of the high-pass filter is lower than the comparison frequency, the vC
It becomes possible to eliminate fluctuations in O output.

Although the oscillation circuit of this embodiment has been explained using a common collector Colpitts type oscillator circuit, it is obvious that any oscillator using a variable capacitance diode in the resonant circuit can be applied.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to widen the PLL loose band to the comparison frequency component of the phase comparator, and at the same time realize vCO with less output frequency nKwJ due to the comparison frequency component included in the frequency 1tilI# voltage. be able to.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention. In the figure, 11... Frequency type control voltage input, 12...
・DC amplifier, 13... High pass filter, 1
4... Phase tA circuit, 15... Amplitude adjustment circuit, 16. L8, 23...DC cut capacitor, 17...Variable capacitance diode, 19
...Inductor, 20,21'-...Feedback capacitor, 22...Transistor, 24.
...■CO output terminal.

Claims (1)

[Claims] A voltage controlled oscillator for PLL uses a variable capacitance diode in a resonant circuit and controls the oscillation frequency by applying a control voltage to one end of the variable capacitance diode, the other end of the variable capacitance diode having a high-pass filter; A voltage controlled oscillator for PLL, characterized in that the frequency control voltage is applied through a phase adjustment circuit and an amplitude adjustment circuit to which the output of the filter is connected.