JP2001332971A - Pll frequency synthesizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a miniaturized and inexpensive switching PLL frequency synthesizer by reducing the number of parts to have a single low-pass filter(LPF) shared among plural voltage controlled oscillators (VCO). SOLUTION: The LPF 3 is connected to a charge pump output terminal 2 of a PLL-IC 1 and a control voltage terminal 5a of a VCO 4a, having an operation control terminal 6a and a control voltage terminal 5b of a VCO 4b having an operation control terminal 6b are connected in parallel to the LPF 3. By selectively switching the output current of a charge pump circuit 7 built in the PLL-IC 1 and the operation control terminals 6a and 6b of the VCO 4a and 4b, the PLL frequency synthesizer having different frequency bands can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PLL frequency synthesizer used for a mobile communication device such as a mobile phone or a mobile phone.

[0002]

2. Description of the Related Art A conventional switched PLL frequency synthesizer will be described below. Conventional switchable PLL
The frequency synthesizer was as shown in FIG. That is, a PLL-IC whose charge pump current cannot be controlled.
(A frequency divider, a comparison circuit, and a charge pump are integrated in this IC.) 11 A charge pump output terminal 12 is provided with a switch 14, and this switch 1
The output of 4 is connected to low-pass filters 13a and 13b, and the outputs of low-pass filters 13a and 13b have a control voltage terminal 5a of a voltage controlled oscillator 4a having an operation control terminal 6a and an operation control terminal 6b, respectively. The configuration is such that the voltage control oscillator 4b is connected in parallel to the control voltage terminal 5b. Then, different oscillation frequencies are output by switching the changeover switch 14 and switching the operation voltage to the operation control terminals 6a and 6b.

[0003]

However, in such a conventional configuration, the switch 14 for switching the PLL loop and the low-pass filter 1 having different pass characteristics are used.
There is a problem in that two sets of 3a and 13b are required, and the shape becomes large as the number of parts increases.

An object of the present invention is to solve such a problem and to provide a small PLL frequency synthesizer with a small number of components.

[0005]

SUMMARY OF THE INVENTION In order to achieve this object, the present invention provides a voltage controlled oscillator comprising a plurality of voltage supply means connected in parallel and selectively supplying a voltage to an operation control terminal. And a comparison circuit in which the outputs of the plurality of voltage controlled oscillators are supplied to one input and the output of the reference oscillator is connected to the other input, and the output current of the comparison circuit is connected to the output of the comparison circuit. A PLL loop formed by a selected voltage controlled oscillator formed by a charge pump circuit having control means and a low pass filter connected between an output of the charge pump circuit and a control voltage terminal of the voltage controlled oscillator. Are controlled by the output current of the charge pump circuit.

Thus, the size of the PLL frequency synthesizer can be reduced.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a voltage controlled oscillator provided with voltage supply means connected in parallel and having a voltage selectively supplied to an operation control terminal. A comparison circuit in which the outputs of the plurality of voltage controlled oscillators are supplied to one input and the output of the reference oscillator is connected to the other input, and the output of the comparison circuit is connected to the output of the comparison circuit to control the output current. And a low-pass filter connected between the output of the charge pump circuit and the control voltage terminal of the voltage controlled oscillator, the PLL loop being formed by the selected voltage controlled oscillator. A PLL frequency synthesizer for controlling a characteristic value by an output current of the charge pump circuit, wherein a characteristic value of a PLL loop is controlled by an output current of the charge pump circuit. And, the low-pass filter can be miniaturized enables shared. Also,
By sharing the filter, the number of parts is reduced and the manufacturing cost is reduced.

According to a second aspect of the present invention, the relationship between the number of divisions of the frequency divider inserted into the input of the comparison circuit, the charge pump current, and the control voltage sensitivity of the voltage controlled oscillator is expressed by the following equation. 2. The PLL frequency synthesizer according to claim 1, wherein the cutoff frequency and the noise removal characteristic in a plurality of sets of PLL loops are made substantially equal, and the characteristics when the voltage controlled oscillator is switched become substantially equal.
By incorporating an L frequency synthesizer, performance can be made uniform by switching devices.

[0009]

(Equation 2)

(Embodiments) The present invention will be described below with reference to the drawings. FIG. 1 shows a PL according to an embodiment of the present invention.
2 shows a block configuration of an L frequency synthesizer. In the present embodiment, the low-pass filter 3 is connected to the output terminal 2 of the charge pump circuit 7 built in the PLL-IC 1.
And the output of the low-pass filter 3 is connected to a control voltage terminal 5 of a voltage controlled oscillator 4a having an operation control terminal 6a.
a and connected in parallel to the control voltage terminal 5b of the voltage controlled oscillator 4b having the operation control terminal 6b. By selectively switching the output current of the charge pump circuit 7 incorporated in the PLL-IC 1 and the operation control terminals 6a and 6b of the voltage controlled oscillator 4a and the voltage controlled oscillator 4b, a PLL frequency synthesizer having different frequency bands is configured. .

According to the above-described embodiment, the voltage controlled oscillators 4a and 4b having different frequency bands and control sensitivities.
Is used, the cutoff frequency and the noise removal characteristic in the PLL loop can be switched by controlling the current by the charge pump control terminal 8 of the charge pump circuit 7. A PLL frequency synthesizer sharing the pass filter 3 can be configured.

Further, by setting the charge pump current, the control voltage sensitivity of the voltage controlled oscillators 4a and 4b, and the frequency division number of the PLL-IC1 to [Equation 3], the cutoff frequency in the two sets of PLL loops is reduced. The noise removal characteristics can be made equal, and the same lock-up time and C / N characteristics can be obtained even when voltage controlled oscillators having different frequency bands and voltage control sensitivities are used.

[0013]

(Equation 3)

[0014]

As described above, according to the present invention, PLL-
The cut-off frequency and noise elimination characteristics are variable by controlling the current by the charge pump circuit of the IC, so the number of parts used can be reduced without deteriorating the performance. A synthesizer can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of a PLL frequency synthesizer according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional PLL frequency synthesizer.

[Explanation of symbols]

 Reference Signs List 1 PLL-IC 2 Charge pump output terminal 3 Low pass filter 4a Voltage controlled oscillator 4b Voltage controlled oscillator 5a Control voltage terminal 5b Control voltage terminal 6a Operation control terminal 6b Operation control terminal 7 Charge pump circuit 8 Charge pump control terminal

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J106 AA04 BB01 CC20 CC24 CC38 CC41 CC52 DD32 GG15 HH03 KK38 KK39 PP03 PP05 QQ12 RR17

Claims (2)

[Claims] 1. A voltage-controlled oscillator comprising a plurality of voltage-controlled oscillators connected in parallel and selectively supplied with a voltage to an operation control terminal; A comparison circuit connected to the output of the reference oscillator at the other input, a charge pump circuit connected to the output of the comparison circuit and having output current control means, and an output of the charge pump circuit. And a low-pass filter connected between the voltage-controlled oscillator and a control voltage terminal of the voltage-controlled oscillator, wherein the PLL controls the characteristic value of the PLL loop by the selected voltage-controlled oscillator with the output current of the charge pump circuit. Frequency synthesizer. 2. A plurality of sets of PLLs by setting the division number of a frequency divider inserted into the input of the comparison circuit, the charge pump current, and the control voltage sensitivity of the voltage controlled oscillator to [Equation 1].
2. The PLL frequency synthesizer according to claim 1, wherein a cutoff frequency in the loop is substantially equal to a noise removal characteristic. (Equation 1)