JP2001292063A - Frequency synthesizer and mobile wireless unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a frequency synthesizer that selects a frequency at a very high-speed in the case of measuring the electric field strength of a signal transmitted from a surrounding base station without deteriorating the basic performance of the frequency synthesizer for a usual communication period. SOLUTION: The frequency synthesizer controlling an oscillated frequency of a voltage controlled oscillator with an output of a loop filter, is provided with a 1st circuit having a 1st charge pump supplying a 1st drive current and a 1st loop filter connected to the 1st charge pump and having a 1st time constant, a 2nd circuit having a 2nd charge pump supplying a 2nd drive current larger than the 1st drive current and a 2nd loop filter connected to the 2nd charge pump and having a 2nd time constant smaller than the 1st time constant, a switch that connects either of the 1st anal 2nd circuits between the phase comparator and the voltage controlled oscillator depending on a communication period and a control means that applies switching control to the switch.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency synthesizer for switching a frequency used in a mobile radio device such as a portable telephone.

[0002]

2. Description of the Related Art In recent mobile radio communication systems, a time division multiple access (TDMA) system has been adopted as a communication system between a mobile station such as a portable telephone and a base station. FIG. 3 shows an example of the configuration of the mobile radio communication system. 3, 101 to 107 are base stations, 110 is a base station 10
The mobile station moves within one wireless zone. Base station 10
Each of the base stations 1 to 107 forms an independent radio zone, and a different radio frequency is assigned to each base station. In the example shown in the figure, the base stations 101 to 107 are assigned radio frequencies F1 to F7, respectively. I have. The mobile station 110 communicates with the base station 101 by selecting an empty time slot from each time slot of a signal transmitted on the communication channel of the radio frequency F1.

A mobile station 110 located in a radio zone of the base station 101 transmits a signal transmitted from a peripheral base station during a vacant time slot other than a time slot used for transmission / reception to / from the base station 101. The electric field strength is measured, and the result is periodically returned to the base station 101. Then, channel switching is performed as necessary.

FIG. 4 shows an example of the structure of a time slot, in which one frame has six slots (for example, one slot: 15).
ms). The mobile station 110 communicates with the base station in the wireless zone where the mobile station is currently located during the transmission slot and the reception slot period, receives the signals of the peripheral base stations at Tms during the idle slot period, and measures the electric field strength. In the example of FIG. 3, the surrounding base stations 102 to 107 are set at Tms.
(Each of the radio frequencies F2 to F7) is received, and each electric field strength is measured.

FIG. 5 is a block diagram showing a configuration of a mobile phone as an example of a mobile station. In FIG. 5, reference numeral 201 denotes a reception unit that receives a radio signal from a base station via an antenna, 202 denotes a reception signal processing circuit, 203 denotes a reception unit such as a speaker, and 204 transmits a radio signal to the base station via an antenna. A transmission unit, 205 is a transmission signal processing circuit, 206 is a transmission unit such as a microphone, 207 is a frequency synthesizer, and 208 is a control circuit.

[0006] The receiving section 201 amplifies the received radio signal and demodulates it into a baseband signal. The baseband signal is converted into a voice signal by a reception signal processing section 202 and a voice is output from a reception section 203. The voice input from the transmitting section 206 is converted into a baseband signal by the transmission signal processing circuit 205, and the transmitting section 204 modulates and amplifies the radio signal and transmits the signal via an antenna. The frequency synthesizer 207 has a function of switching and generating a large number of frequencies in accordance with the frequency of a channel for transmission and reception. The control circuit 208 controls the circuit operations of the reception signal processing circuit 202 and the transmission signal processing circuit 205, The frequency switching of the synthesizer 207 is controlled.

FIG. 6 is a block diagram showing a configuration of a conventional frequency synthesizer. 6, reference numeral 1 denotes a reference frequency oscillator, 2 denotes a first frequency divider, 3 denotes a phase comparator, 5 denotes a charge pump, 6 denotes a loop filter, 8 denotes a voltage controlled oscillator (VCO), and 11 denotes a second frequency divider. The circulator 13 is a control unit.

The reference frequency signal output from the reference frequency oscillator 1 is frequency-divided by the first frequency divider 2 and input to the phase comparator 3. On the other hand, the oscillation output signal output from the voltage controlled oscillator 8 is frequency-divided by the second frequency divider 11 and fed back to the phase comparator 3. Here, the frequency division number of the first frequency divider 2 is fixed, and the frequency division number of the second frequency divider 11 is variable.
Is set to the frequency division number according to the frequency assigned to the base station that performs transmission and reception by the control signal from the base station. The phase comparator 3 receives the output of the first frequency divider 2 and the output of the second frequency divider as inputs, detects a phase difference between them, and performs a charge pump 5 operation.
Output to The charge pump 5 converts the output of the phase comparator 3 into a drive signal for a loop filter 6 which is an integrator,
From the loop filter 6, a DC voltage corresponding to the phase difference is supplied to the voltage controlled oscillator as a control voltage. Thereby, the oscillation output signal from the voltage controlled oscillator 6 is controlled to the target frequency.

In such a conventional frequency synthesizer, the loop filter 6 is formed of, for example, a CR circuit and has a predetermined time constant. Further, when this time constant is reduced, frequency switching can be performed at high speed. However, there is a problem that a noise bandwidth is widened and S / N and C / N as a frequency synthesizer are deteriorated. The constant cannot be too small. Therefore, in a system with a high signal transmission rate or in a case where the vacant time slot period in one frame is short, it takes time to switch the frequency, and it is not possible to take sufficient time to measure the electric field strength of a signal transmitted from a peripheral base station. There was a problem that.

As a prior art for solving this problem, Japanese Patent Application Laid-Open No. 4-142815 discloses a first loop filter used during a normal communication period and a first loop filter used for measuring electric fields of peripheral base stations.
There is a method of switching and using a second loop filter having a smaller time constant than the time constant of the loop filter. However, in recent years, as communication forms have diversified and the number of communication channels has increased dramatically, The need for high-speed communication has increased, and it has become necessary to perform frequency switching at an extremely high speed.

[Problems to be solved by the invention]

According to the present invention, when measuring the electric field strength of a signal transmitted from a peripheral base station without deteriorating the basic performance of the frequency synthesizer during a normal communication period, a frequency at which the frequency can be switched at a very high speed can be obtained. The purpose is to provide a synthesizer.

[0012]

According to a first aspect of the present invention, there is provided a phase comparator for detecting a phase difference between an oscillation output of a reference oscillator and an output obtained by variably dividing the oscillation output of a voltage controlled oscillator. A charge pump that converts the output to drive current,
A frequency synthesizer that receives the output of the charge pump as input and generates a DC voltage according to the phase difference, and controls the oscillation frequency of the voltage-controlled oscillator by the output of the loop filter. A first circuit comprising a first charge pump for supplying, a first loop filter connected to the first charge pump and having a first time constant, and a second drive greater than the first drive current A second charge pump for supplying current and the first charge pump connected to the second charge pump;
And a second circuit including a second loop filter having a second time constant smaller than the time constant of any one of the first circuit and the second circuit according to a communication period. A switch connected between the switch and the voltage-controlled oscillator, and control means for switching and controlling the switch.

According to a second aspect of the present invention, a mobile radio apparatus includes the frequency synthesizer according to the first aspect.

According to a third aspect of the present invention, in the mobile radio device according to the second aspect, the first circuit is selected when communicating with a base station in a radio zone where the mobile radio device is located. The second circuit is selected when measuring the electric field strength of the peripheral base station.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. In FIG. 1, the same parts as those in FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted. Reference numeral 4 denotes a first switch, 5 denotes a first charge pump (same as the charge pump 5 in FIG. 6), 6 denotes a first loop filter (same as the loop filter 6 in FIG. 6), and 7 denotes a second loop filter. The switch 9 is a second charge pump which supplies a larger drive current than the first charge pump 5 to the loop filter. Reference numeral 10 denotes a second loop filter having a time constant smaller than that of the first loop filter 6. 1
2 is a control unit.

Next, the operation will be described. The output of the phase comparator 3 is connected to one of the input of the first charge pump 5 and the input of the second charge pump 9 by the first switch 4. Further, the input of the voltage controlled oscillator 8 is connected to one of the output of the first loop filter 6 and the output of the second loop filter 10 by the second switch 7.

FIG. 2 shows a control procedure and control contents of the frequency synthesizer. First, during a normal communication period, the output of the phase comparator 3 is input to the input of the first charge pump 5 by the first switch 4, and the output of the first loop filter 6 is output to the input of the voltage controlled oscillator 8 by the second switch 7. Each is connected to an input. The operation of the frequency synthesizer at this time is the same as that described with reference to FIG. 6, and a detailed description thereof will be omitted.

In step 51, the control circuit 12 monitors whether or not it is during the electric field measurement period of the peripheral base station.
And the second switch 7. In step 52, the first electric field detection mode switching signal (OFF → ON)
The switch 4 and the second switch 7 are linked with each other, and the output of the phase comparator 3 is input to the input of the second charge pump 9 by the first switch 4, and the input of the voltage controlled oscillator 8 is input to the second switch 7 by the second switch 7. 2 are respectively connected to the outputs of the loop filters 10. In step 53, a frequency corresponding to a peripheral base station for which an electric field is measured is set in the second frequency divider 11. After performing the electric field measurement for a predetermined time t in step 54, it is determined in step 55 whether to perform the electric field measurement of another frequency (next base station). Here, if the electric field measurement of another frequency is not performed, that is, if the electric field measurement period ends, the control circuit 12 sends the electric field detection mode switching signal to the first in step 56.
The first switch 4 and the second switch 7 are linked by the electric field detection mode switching signal (ON → OFF), and the phase comparator 3 is Is connected to the input of the first charge pump 5, and the input of the voltage controlled oscillator 8 is connected to the output of the first loop filter 6 by the second switch 7. If it is not the electric field measurement period in step 51, the frequency division number corresponding to the frequency assigned to the base station in communication by the control signal from the control unit 12 is set in the second frequency divider 2 in step 57.

Since the second loop filter 10 has a time constant smaller than the time constant of the first loop filter 6, the frequency of the second loop filter 10 is switched when the second loop filter 10 is used as compared with when the first loop filter 6 is used. Is faster. The second charge pump 9 is a first charge pump 5
Since a larger drive current is supplied to the loop filter, the charge / discharge of the loop filter is faster when the second charge pump is used than when the first charge pump 9 is used, and the frequency switching can be made faster. it can.

Therefore, when measuring the electric field of the peripheral base station, the first
Switch 4 and the second switch 7 are linked, and the second switch 7
Since the charge pump 9 and the second loop filter 10 are used, the frequency can be switched faster than at the time of normal transmission / reception in which the first charge pump 5 and the first loop filter 6 are used.

Note that the second charge pump 9 and the second charge pump
When the loop filter 10 is used, that is, when measuring the electric field of the peripheral base station, high-speed frequency switching is possible, while the noise bandwidth is widened and S / N and C / N as frequency synthesizers are used.
However, since there is no need to demodulate the received signal and only the intensity of the electric field needs to be measured, there is no particular problem.

[0022]

As described above, the present invention provides a phase comparator for detecting the phase difference between the oscillation output of the reference oscillator and the output obtained by variably dividing the oscillation output of the voltage controlled oscillator, and the output of the phase comparator. A charge pump for converting and driving current, a loop filter for receiving an output of the charge pump as input and generating a DC voltage corresponding to the phase difference, and controlling an oscillation frequency of the voltage controlled oscillator by an output of the loop filter. A first circuit including a first charge pump for supplying a first drive current, a first loop filter connected to the first charge pump, and having a first time constant; A second charge pump for supplying a second drive current larger than the drive current and connected to the second charge pump and smaller than the first time constant A second circuit comprising a second loop filter having a time constant of 2; and the phase comparator and the voltage-controlled oscillator according to one of the first circuit and the second circuit according to a communication period. A switch connected between the
By providing the control means for switching the switch, when the second circuit is selected, the frequency can be switched at a very high speed.

In addition, by providing the mobile radio apparatus with the frequency synthesizer of the present invention, the basic performance of the frequency synthesizer during a normal communication period is not degraded, and it takes time to switch the frequency, and the base station from the surrounding base station is not required. The measurement of the electric field strength of the transmitted signal does not take much time, and the frequency can be switched at high speed only when measuring the electric field strength of the signal transmitted from the surrounding base station. It is possible to provide a mobile radio apparatus that can cope with a fast system or a case where an empty time slot period in one frame is short.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of a frequency synthesizer showing an embodiment of the present invention.

FIG. 2 is a flowchart showing a control procedure and control contents of a frequency synthesizer according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of a configuration of a mobile radio communication system of a time division multiple access (TDMA) system.

FIG. 4 is a diagram illustrating an example of a time slot configuration of a time division multiple access (TDMA) system.

FIG. 5 is a block diagram illustrating a configuration of a mobile phone as an example of a mobile station.

FIG. 6 is a block diagram of a conventional frequency synthesizer.

[Explanation of symbols]

1 reference frequency oscillator, 2 first divider, 3 phase comparator, 4 first switch, 5 first charge pump, 6 first loop filter, 7 second switch,
8 is a voltage controlled oscillator (VCO), 9 is a second charge pump, 10 is a second loop filter, 11 is a second frequency divider, 12 control unit

Claims (3)

[Claims] 1. A phase comparator for detecting a phase difference between an oscillation output of a reference oscillator and an output obtained by variably dividing an oscillation output of a voltage controlled oscillator, a charge pump for converting an output of the phase comparator to a drive current, A frequency synthesizer that receives an output of the charge pump as input and generates a DC voltage according to the phase difference, and controls an oscillation frequency of the voltage-controlled oscillator by an output of the loop filter; A first circuit comprising a first charge pump to be supplied, a first loop filter connected to the first charge pump and having a first time constant, and a second drive greater than the first drive current A second charge pump for supplying current and a second loop connected to the second charge pump and having a second time constant smaller than the first time constant; A switch that connects one of the first circuit and the second circuit between the phase comparator and the voltage-controlled oscillator according to a communication period; and A frequency synthesizer, comprising: control means for performing switching control; 2. A mobile radio apparatus comprising the frequency synthesizer according to claim 1. 3. The mobile radio apparatus according to claim 2, wherein the first circuit is selected when communicating with a base station in a radio zone where the mobile radio apparatus is located, and the electric field of a peripheral base station is selected. A mobile radio apparatus, wherein the second circuit is selected at the time of intensity measurement.