JPH0529931A - Frequency synthesizer - Google Patents

Abstract

PURPOSE:To quicken the frequency changeover of the frequency synthesizer. CONSTITUTION:The frequency synthesizer comprising a phase locked loop in which a comparator signal based on an output of a frequency variable controlled oscillator 30 and a reference signal based an output of a reference oscillator 31 are subjected to phase comparison at a phase comparator 32 and a phase difference signal is given to a loop filter 33 and used for a control signal for the controlled oscillator 30 is provided with a storage section 34 storing a data relating to a control signal of the controlled oscillator 30 corresponding to each output frequency for the synthesis of the frequency synthesizer. Then it is featured that when the output frequency of the frequency synthesizer is switched, a data corresponding to the output frequency after the changeover as the pre-processing is read out of the storage section 34 so that the control signal to the controlled oscillator 30 is a value in response to the read data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency synthesizer, and more particularly to a frequency synthesizer capable of switching output frequency values at high speed.

Such a frequency synthesizer is used as a frequency source for, for example, an automobile telephone. Car phones use the frequency assigned to the zone in which they are located to communicate, but with this,
It is also necessary to monitor the radio wave condition of the adjacent zone in order to know in which zone the self is currently located. For this purpose, a plurality of frequency sources including the frequencies of the surrounding zone in addition to the current zone are required on the side of the car telephone, and a frequency synthesizer is generally used to achieve this purpose. On the other hand, when communicating using, for example, the TDM method, the radio wave condition of the adjacent zone should be monitored by switching the frequency to the adjacent zone frequency one after another in a short time zone other than the time slot used by the communication itself. become. Therefore, the frequency synthesizer is required to be able to switch the output frequency at high speed one after another.

[0003]

2. Description of the Related Art An example of the configuration of a conventional frequency synthesizer is shown in FIG. Here, this frequency synthesizer is used as a frequency source for an automobile telephone, and this automobile telephone has a function of performing battery power saving in a standby state.

In FIG. 5, reference numeral 1 is a reference oscillator for generating a highly stable reference frequency, and here, for example, 12.8M.
It is assumed that Hz is oscillated. Reference numeral 2 is a reference frequency divider that divides the reference frequency of the reference oscillator 1. Here, 12.8M
Hz and divides the reference signal f _r of 25 kHz. Reference numeral 3 denotes a phase comparator, which is a comparison signal f from a comparison frequency divider 8 described later.
_v performs phase comparison of the reference signal f _r from the reference frequency divider 2 and provides the phase difference signal (phase lead signal and a phase lag signal) to the charge pump 4.

Reference numeral 5 denotes a loop filter section, which is a resistor 5
1, 52 and a capacitor 53, which is a low-pass filter.
Controlled by. The output signal of the loop filter unit 5 is input to the voltage controlled oscillator 6 as a control voltage. Here, the voltage controlled oscillator 6 is a circuit that oscillates a variable frequency of about 1.5 GHz, and its oscillation output serves as an output signal of the signal synthesizer and is input to the comparison frequency divider 8 via the prescaler 7. The prescaler 7 is a circuit that divides the oscillation frequency in the 1.5 GHz band from the voltage controlled oscillator 6 into an appropriate size of about 10 MHz, and the comparison frequency divider 8 outputs the output signal from the prescaler 7 at 25 kHz.
It is a circuit that divides the frequency of the comparison signal f _v .

Reference numeral 9 denotes a forced phase synchronizing circuit. The forced phase synchronizing circuit 9 locks up at a desired output frequency at high speed by the frequency synthesizer when the frequency synthesizer is started, for example, when power save is switched from ON to OFF. It is a circuit for performing such control. Specifically, by referring to the comparison signal f _v of the comparison frequency divider 8, the reference frequency division is forcibly performed so that the phase of the reference signal f _r of the reference frequency divider 2 matches the phase of the comparison signal f _v. It is a circuit for adjusting the phase of the device 2. Normally, when the power save is turned on, the control voltage of the voltage controlled oscillator 6 is held at the value just before the power save is turned on. Therefore, even after the power save is turned off, the frequency of the comparison signal f _v is the reference. It is kept the same as the frequency of the signal _fr , but there is a phase difference. The forced phase synchronization circuit 9 shortens the lead-in time of the frequency synthesizer by forcibly setting the phase difference to zero.

In the above-mentioned circuit, a circuit 20 surrounded by a double line in the figure, that is, a reference frequency divider 2, a phase comparator 3, a charge pump 4, a comparison frequency divider 8, and a forced phase synchronization circuit 9 is used. The formed circuit is usually configured as one IC, and a frequency synthesizer is configured by combining such an IC circuit 20, the reference oscillator 1, the loop filter unit 5, the voltage controlled oscillator 6, the prescaler 7, and the like.

In this frequency synthesizer, the IC circuit 2
The clock CLK, the data DATA, the strobe signal STB, and the power save signal PS are input to 0. By changing the division ratio of the reference frequency divider 2 and the comparison frequency divider 8 by this data DATA, the output of the frequency synthesizer is output. Changing the frequency.

[0009]

In the conventional frequency synthesizer, the pull-in speed can be increased by the above-mentioned forced phase synchronizing circuit 9 when returning from the power save. However, when frequency switching is performed, the time from the switching to the frequency synchronization and phase synchronization of the phase-locked loop to the target frequency is determined by the time constant of the loop filter and the transfer function of each circuit. . In this case, since the loop filter takes some time to charge and discharge the capacitor, it takes time to switch the frequency. For this reason, for example, the demand for speeding up the frequency switching necessary for the above-mentioned automobile telephones has not been sufficiently satisfied.

The present invention has been made in view of the above circumstances, and an object of the present invention is to speed up frequency switching of a frequency synthesizer.

[0011]

FIG. 1 is a diagram illustrating the principle of the present invention. The frequency synthesizer according to the present invention is
As a basic form, a variable frequency control type controlled oscillator 3
The comparison signal based on the output of 0 and the reference signal based on the output of the reference oscillator 31 are phase-compared by the phase comparator 32, and the phase difference signal is passed through the loop filter 33 to the controlled oscillator 30.
In a frequency synthesizer configured with a phase locked loop as a control signal of, a storage unit 34 that stores data regarding the value of the control signal of the controlled oscillator 30 corresponding to each output frequency synthesized by the frequency synthesizer,
When switching the output frequency of the frequency synthesizer, the data corresponding to the output frequency after switching is read from the storage unit 34 as a pre-process, and the value of the control signal to the control oscillator 30 becomes a value according to the read data. It is characterized by doing so.

Further, the frequency synthesizer according to the present invention is
As another mode, in the above-described basic mode, the setting operation of the control signal of the controlled oscillator 30 in the preprocessing is performed by charging and discharging the capacitor of the loop filter 33.

Further, the frequency synthesizer according to the present invention is
As another mode, in each of the above modes, a temperature sensor 35 for detecting the ambient temperature is provided, and data corresponding to the output frequency of the frequency synthesizer is stored in the storage unit 34 for each temperature, and the output of the frequency synthesizer is stored. When the frequency is switched, the data corresponding to the temperature detected by the temperature sensor 35 is read from the storage unit 34.

Further, the frequency synthesizer according to the present invention is
As another mode, in each of the above modes, a detection unit 36 that detects the internal voltage of the loop filter 33 and a writing unit 37 that writes the internal voltage detected by the detection unit to the storage unit 34 are provided, and the storage unit 34 includes , The detection unit 36 corresponding to each state
The internal voltage detected in 1 is previously written as data corresponding to the control signal.

[0015]

When the frequency is switched, first of all, as a pre-process, the controlled oscillator 30 corresponding to the frequency of the switching destination is used.
Reading the data relating to the control signal from the storage unit 34,
It is preset so that the value of the control signal of the controlled oscillator 30 becomes a value corresponding to the frequency of the switching destination. This shortens the frequency pull-in time and speeds up frequency switching.

The ambient temperature is detected by a temperature sensor,
By reading the data corresponding to the temperature from the storage unit 34, the error due to the difference in ambient temperature can be eliminated and more accurate control can be performed.

As a method of setting data in the storage unit 34, for example, the actual internal voltage of the loop filter 33 is measured by the detection unit 36 for each output frequency of the frequency synthesizer, and this is written by the writing unit 37 in the storage unit 37. Can be written to.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows a frequency synthesizer as an embodiment of the present invention. This frequency synthesizer is used as a frequency source for automobile telephones as described above, and has a power saving function. In the figure, a reference oscillator 1, a reference frequency divider 2, a phase comparator 3, a charge pump 4,
The loop filter unit 5, the voltage controlled oscillator 6, the prescaler 7, the comparison frequency divider 8, and the forced phase synchronization circuit 9 are the same as those described in the above-mentioned conventional technique.

As a difference from the conventional circuit, the embodiment circuit is provided with a control circuit 10, a ROM 11, a D / A converter 12, an amplifier 13, switches 14, 15, an A / D converter 16 and a temperature sensor 17. There is. The clock CLK, the data DATA, the strobe signal STB, and the power save signal PS are input to the control circuit 10, and the detected temperature value is input from the temperature sensor 17. Based on these, ON / OFF of the switches 14 and 15 is turned on. Control and ROM 11
Address is specified.

The ROM 11 is an EEPROM or the like, and the loop filter section 5 is outputting to the ROM 11 for each temperature corresponding to each value of the output frequency which can be set by the frequency synthesizer. The terminal voltage value Vc of the internal capacitor 53 (which is substantially the control voltage of the voltage controlled oscillator 6) is stored in the form of a table. The method of setting this table will be described in detail later.

The terminal voltage data read from the ROM 11 is converted into an analog signal through the D / A converter 12, and then, through the amplifier 13 and the switch 14 at the time of ON, the capacitor 53 of the loop filter section 5 is converted. It can be applied to the terminals. The terminal of the capacitor 53 is connected to the A / D converter 16 via the switch 15 so that the terminal voltage value Vc of the capacitor 53 can be converted into a digital signal. This A / D
The output signal from the converter 16 is input to the ROM 11 as write data.

The operation of the circuit of this embodiment will be described below with reference to FIG. Here, FIG. 4 is a time chart of signals at various parts of the embodiment circuit, in which (a) is data DATA and (b).
Is a clock CLK, (c) is a strobe signal STB,
(D) is the power save signal PS, (e) is the address signal input to the ROM 11, and (f) is the switch 14 ON.
A switch signal SW for controlling ON / OFF, (g) is a terminal voltage value Vc of the capacitor 53 in the loop filter unit 5.
Is.

The basic operation of the circuit of this embodiment is the same as that of the conventional example. That is, the data DATA input to the IC circuit 20 sets the frequency division ratios of the reference frequency divider 2 and the comparison frequency divider 8 so that the frequency synthesizer outputs a desired frequency. Output signal outputted from the reference oscillator 1 is divided into a reference signal f _r by a reference frequency divider 2 is input to one of the phase comparator 3, also from the voltage controlled oscillator 6 and the other phase comparator 3 The output signal output is frequency-divided into the comparison signal f _v by the comparison frequency divider 8 and is input. The phase comparator 3 compares the phases of the input two input signals and drives the charge pump 4 according to the phase difference between the two input signals, thereby charging and discharging the capacitor 53 of the loop filter unit 5. The output signal output from the loop filter unit 5 is applied to the voltage controlled oscillator 6 as a control voltage, whereby a phase locked loop is formed,
Phase synchronization and frequency synchronization are achieved.

Here, it is assumed that the frequency is switched to another value. When this frequency switching is performed, first, the power save signal PS is input to the IC circuit 20, whereby the frequency synthesizer enters the power save state. After that, when the clock CLK, the data DATA, and the strobe signal STB are input from the outside, based on the data DATA, the reference frequency divider 2 and the comparison frequency divider 8 are set to the frequency to be newly set next. The corresponding division ratio is set.

These clock CLK, data DATA,
The strobe signal STB is also input to the control circuit 10, whereby the control circuit 10 reads from the ROM 11 the data of the terminal voltage value Vc of the capacitor 53 of the loop filter unit 5 corresponding to the frequency to be set next by the frequency synthesizer. Address to ROM 11. . Note that this data is addressed to correspond to the temperature from the temperature sensor 17.

As a result, the data corresponding to the frequency of the switching destination is read from the ROM 11, and this data is D /
The amplifier 1 after being converted into an analog value via the A converter 12
3 is input to the switch 14. This switch 1
The switch signal SW from the control circuit 10 turns on 4 at an appropriate timing during power saving, whereby the data read from the ROM 11 is converted into an analog value and the capacitor of the loop filter unit 5 is passed through the switch 14. It will be applied to the terminal of 53. As a result,
The terminal voltage value of the capacitor 53 of the loop filter unit 5 is
It is charged and discharged so as to match the value corresponding to the data read from the ROM 11. This value is the terminal voltage value of the capacitor 53 (that is, the control voltage of the voltage controlled oscillator 6) when the frequency synthesizer stabilizes at the frequency of the switching destination.

Next, when the power save signal PS is turned off and the power save state is released, the switch 14 is turned off.
It becomes FF, so that the capacitor 53 switches the switch 14
It is disconnected from the circuit on the side, and normal operation is started so as to be frequency-synchronized and phase-synchronized with the frequency of the switching destination.

As described above, in the embodiment circuit, the capacitor 5 of the loop filter unit 5 is in the power saving state.
3, the control voltage of the voltage controlled oscillator 6 for setting the frequency of the switching destination is charged to match the frequency of the voltage controlled oscillator 6, and then the power save state is released to set the forced phase in the IC circuit 20. Since the phase synchronization is immediately performed by the synchronizing circuit 9, the pull-in time at the time of frequency switching can be extremely short, and the frequency switching can be speeded up.

In the circuit of this embodiment, the temperature sensor 17
Since the ambient voltage is measured by and the terminal voltage value set in the capacitor 53 of the loop filter unit 5 is controlled according to the ambient temperature, the error in the set voltage to the capacitor 53 due to the difference in ambient temperature is reduced. It can be reduced.

There are various ways of configuring the switch 14 of the embodiment circuit, for example, [A] in FIG.
As shown in, when FET is used, when increasing the frequency, FET1 is turned on to charge the capacitor 53 of the loop filter unit 5, and when decreasing frequency, FET2 is turned on and the capacitor 53 of the loop filter unit 5 is changed. Discharge
When not switching, turn off both FET1 and FET2
Then, the phase-locked loop is not affected. Alternatively, as shown in FIG. 3B, two switch elements are used, and when the frequency is switched, the switch SW4 is turned on to discharge the capacitor 53 of the loop filter unit 5 and then turned off, and the switch SW3 is turned on. The capacitor 53 of the loop filter unit 5 is charged with a predetermined voltage by turning it on, and both are turned off when switching is not performed so that the phase locked loop is not affected.

Next, a method of setting the data table in the ROM 11 in the embodiment circuit will be described. This setting is made at the time of product shipment, for example.

First, the power is turned on and a write signal is given to the control circuit 10, whereby the control circuit 10 sets the ROM 11 in the write mode and turns on the switch 15.
If there are now 1000 channels, for example, 1
About 1000 channels are sequentially set from about 4 channels, and the control voltage of the loop filter unit 5 at each frequency (that is, the terminal voltage of the capacitor 53) is input to the A / D converter 16 through the switch 15. Is converted into digital value control voltage data, and this control voltage data is written in the ROM 11. This control voltage data is written in the address position corresponding to the output frequency at that time. As a result, the data in the ROM 11 can be automatically written.

The data writing process as described above is performed for various temperatures by changing the ambient temperature, and R corresponding to each temperature is set.
Create an OM table. Then, as described above, during the operation of the frequency synthesizer, the ambient temperature is detected by the temperature sensor 17, and the control voltage is set by using the ROM table suitable for the temperature.

When the writing is completed, the control circuit 10 turns off the switch 15 so as not to affect the phase locked loop, and returns the ROM 11 to the read mode.

Various modifications are possible in implementing the present invention. For example, in the above embodiment, the circuit (switch 1) for automatically setting the control voltage data in the ROM 11 is used.
5, A / D converter 16 and the like) were provided and the data was set by this circuit, but of course the present invention is not limited to this, and it was performed in advance without using the above-mentioned automatic setting circuit. It is also possible to create a correspondence table of the output frequency, the control voltage value, and the temperature by an experiment, and write the data in the ROM 11 according to this correspondence table. However, when the actual control voltage of the loop filter unit 5 is measured in correspondence with the output frequency of the frequency synthesizer as in the embodiment and the table is stored in the ROM table, the circuit constants of the voltage controlled oscillator 6 and the loop filter unit 5 vary. Even if there is, it can be absorbed, so that more accurate control becomes possible.

In the above embodiment, the temperature sensor 17 for suppressing the influence of the ambient temperature is used for the temperature compensation, but of course, the temperature compensation is not performed when the present invention is carried out. May be.

Although the frequency synthesizer of the present invention is used as the frequency source of the automobile telephone in the above-described embodiment, the present invention is not limited to this and the present invention can be applied to various uses.

[0038]

As described above, according to the present invention, it is possible to speed up the frequency switching of the frequency synthesizer.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a block diagram showing a frequency synthesizer as one embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration example of a switch in the embodiment circuit.

FIG. 4 is a time chart of each signal in the circuit of the embodiment.

FIG. 5 is a block diagram showing a conventional example of a frequency synthesizer.

[Explanation of symbols]

1 Reference oscillator 2 reference divider 3 Phase comparator 4 charge pump 5 Loop filter section 6 Voltage controlled oscillator 7 Prescaler 8 comparison divider 9 Forced phase synchronization circuit 10 Control circuit 11 ROM (read-only memory) 12 D / A converter 13 Amplifier 14, 15 switch 16 A / D converter 17 Temperature sensor

Claims (4)

[Claims] 1. A variable frequency control type controlled oscillator (30)
Of the reference signal based on the output of the reference oscillator and the reference signal based on the output of the reference oscillator (31) are compared in phase by the phase comparator (32), and the phase difference signal is used as the control signal of the control oscillator through the loop filter (33). A frequency synthesizer including a phase-locked loop is provided with a storage unit (34) for storing data relating to a control signal value of a controlled oscillator corresponding to each output frequency synthesized by the frequency synthesizer, and the output frequency of the frequency synthesizer. When switching between
As a preprocessing thereof, data corresponding to the output frequency after switching is read from the storage unit so that the value of the control signal to the controlled oscillator becomes a value according to the read data. Synthesizer. 2. The frequency synthesizer according to claim 1, wherein the setting operation of the control signal of the controlled oscillator in the preprocessing is performed by charging and discharging the capacitor of the loop filter. 3. A temperature sensor (35) for detecting an ambient temperature is provided, and data corresponding to the output frequency of the frequency synthesizer is stored for each temperature in the storage unit, and when switching the output frequency of the frequency synthesizer. Is
3. The frequency synthesizer according to claim 1, wherein the data corresponding to the temperature detected by the temperature sensor is read from the storage unit. 4. A detection unit (36) for detecting an internal voltage of the loop filter, and a writing unit (37) for writing the internal voltage detected by the detection unit to the storage unit, the storage unit comprising: The frequency synthesizer according to any one of claims 1 to 3, wherein the internal voltage detected by the detection unit corresponding to each state is pre-written as data corresponding to a control signal.