JPH02100519A - Frequency synthesizer - Google Patents

Abstract

PURPOSE:To improve the stability of a frequency and the purity of an oscillation waveform and to switch an oscillation frequency at a high speed by inserting a band variable filter between a voltage supply means and a voltage control oscillator, setting the width of a pass band width at the time of switching the oscillation frequency and setting it narrow after convergence. CONSTITUTION:For switching the frequency, the alteration of the frequency in a variable frequency divider 2, the alteration of input data in a digital/ analogue converter 6 and the band-alteration of a band variable filter 8 are simultaneously performed, and the width of the pass band of the band variable filter 8 is set to W1 which is wider than W2. Thus, the output voltage of the digital analogue converter 6 is transmitted to an adder 7 at a high speed, and the control voltage of the voltage control oscillator 1 is altered to V2 at the high speed. Thus, the high speed switching of a frequency is attained. After switching, the width of the pass band of the band variable filter 8 is reset to W2. Thus, noise which has occurred in the digital/analogue converter 6 is controlled and the deterioration of a noise characteristic in the output of the voltage control oscillator 1 is prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has high frequency stability and purity of oscillation waveform,
Moreover, the present invention relates to a frequency synthesizer capable of high-speed switching of oscillation frequency. More specifically, using a phase-locked loop,
In order to shorten the convergence time of this phase-locked loop, the present invention relates to a frequency synthesizer configured to supply a voltage to a voltage-controlled oscillator from outside the phase-locked loop when switching the oscillation frequency.

The present invention is particularly suitable for use in local oscillators and outgoing wave oscillators of wireless communication devices.

The present invention improves the purity of the oscillation waveform of a frequency synthesizer by preventing noise from voltage supply means outside the phase-locked loop after switching the oscillation frequency.

[Conventional technology]

FIG. 8 is a block diagram showing a first conventional example of a frequency synthesizer.

This frequency synthesizer is composed of a phase-locked loop, and includes a voltage controlled oscillator 1, a variable frequency divider 2, and a reference oscillator 3.
, a phase comparator 4 and a loop filter 5.

The voltage controlled oscillator 1 changes its oscillation frequency according to the human control voltage. The variable frequency divider 2 outputs a frequency-divided signal obtained by dividing the output of the voltage-controlled oscillator 1. The reference oscillator 3 generates a reference frequency signal that serves as a reference for phase comparison. The phase comparator 4 compares the phases of the reference frequency signal from the reference oscillator 3 and the frequency-divided signal from the variable frequency divider 2, and adjusts the phase of the loop filter 5 so that the phase difference between the two input signals becomes small. Controls charging and discharging. The loop filter 5 is the phase comparator 4
The output is smoothed and output to the voltage controlled oscillator 1.

As a result, the voltage controlled oscillator 1 oscillates at a frequency corresponding to the frequency division number N of the variable frequency divider 2. This frequency is stable. Further, by changing the frequency division number N of the variable frequency divider 2, the oscillation frequency of the voltage controlled oscillator 1 can be selected.

When the frequency division number N of the variable frequency divider 2 is changed, the oscillation frequency of the voltage controlled oscillator 1 is converged by the feedback circuit of the phase locked loop. The convergence time of this oscillation frequency, that is, the time required for switching the frequency, depends on the time constant of the loop filter 5. For this reason, if a time constant that stabilizes the oscillation frequency is selected, there is a drawback that the frequency switching time becomes long.

FIG. 9 is a block diagram showing a second conventional example of a frequency synthesizer.

This conventional example shortens the frequency switching time without depending on the time constant of the loop filter 5 by directly applying a control voltage corresponding to the oscillation frequency of the frequency switching destination to the voltage controlled oscillator 1 from outside the phase-locked loop. It is something to do. Therefore, in addition to the configuration of the first conventional example, a digital-to-analog converter 6, an adder 7, and a control circuit 9 are provided.

At the time of frequency switching, the control circuit 9 changes the frequency division number N of the variable frequency divider 2 and inputs a value corresponding to the oscillation frequency to which the frequency is to be switched to the digital-to-analog converter 6.

Adder 7 adds the output of digital-to-analog converter 6 to the output of loop filter 5 and supplies the added control voltage to voltage-controlled oscillator 1.

Stabilization of the oscillation frequency after switching is performed using a phase-locked loop, as in the first conventional example.

[Problems to be Solved by the Invention] However, if the output of the digital-to-analog converter 6 contains noise, the noise is directly added to the control voltage of the voltage-controlled oscillator 1. In that case, the oscillation frequency of the voltage controlled oscillator 1 is frequency modulated by noise, resulting in a disadvantage that the purity of the oscillation waveform deteriorates.

An object of the present invention is to provide a frequency synthesizer that can prevent deterioration in oscillation purity due to the addition of a digital-to-analog converter.

[Means for solving problems]

According to a first aspect of the present invention, a variable frequency divider provided in a feedback path of a phase-locked loop, and an oscillation frequency control means for controlling an oscillation frequency by switching the frequency division number of the variable frequency divider. This oscillation frequency control means supplies a control voltage corresponding to the switched frequency division number to the voltage controlled oscillator in the phase-locked loop in synchronization with the switching of the frequency division number of the variable frequency divider, and adjusts its oscillation frequency. In the frequency synthesizer, the voltage supply means includes a variable band filter having a variable pass band width, and the oscillation frequency control means narrows the pass band width of the variable band filter after the switching. A frequency synthesizer is provided, the frequency synthesizer including a bandwidth control means.

The voltage supply means includes a digital-to-analog converter, receives the frequency division number of the variable frequency divider or a digital value equivalent thereto, and outputs an analog voltage corresponding to this digital value.

Further, according to the second aspect of the present invention, the voltage supply means is connected to the voltage holding means in the loop filter provided in the phase-locked loop, and the oscillation frequency control means is configured such that the control voltage from the voltage supply means is A frequency synthesizer is provided, characterized in that it includes means for disconnecting the voltage supply means after being stored in the holding means.

A variable frequency divider with reset can be used as the variable frequency divider. In this case, immediately after the control voltage of the voltage controlled oscillator is set to a voltage corresponding to the switching destination frequency, the oscillation frequency control means is configured to control the variable frequency control with reset in synchronization with the rising or falling edge of the reference signal. It is desirable to include means for instantaneously resetting the clock.

[For production]

In the first aspect of the present invention, a variable band filter is inserted between the voltage supply means and the voltage controlled oscillator, and its passband width is set wide when switching the oscillation frequency, and narrowed after convergence. As a result, a quickly rising control voltage is supplied at the time of switching, and after the oscillation frequency is stabilized, noise from the voltage supply means is prevented from being transmitted to the voltage controlled oscillator.

In a second aspect of the invention, the voltage supply means is separated from the phase-locked loop after frequency switching.

〔Example〕

FIG. 1 is a block diagram of a frequency synthesizer according to a first embodiment of the present invention. a phase comparator 4 that compares the output phase of the frequency generator 2 with the phase of the reference signal supplied from the reference oscillator 3; a loop filter 5 that smoothes the output of the phase comparator 4 and supplies it to the voltage controlled oscillator 1; The oscillation frequency control means controls the oscillation frequency of the voltage controlled oscillator 1 by switching the frequency division number of the variable frequency divider 2. This oscillation frequency control means includes a control circuit 9, and when switching the frequency division number of the variable frequency divider 2, supplies a control voltage corresponding to the switched frequency division number to the voltage controlled oscillator 1 to increase its oscillation frequency. As a voltage supply means for rapidly changing the voltage, an analog/digital converter 6, a variable band filter 8 connected to the output of the analog/digital converter 6, and an output of the variable band filter 8 are added to the output of the loop filter 5. An adder 7 is provided.

Here, the feature of this embodiment is that the voltage supply means includes a band variable filter 8 whose pass band width is variable, and the control circuit 9 controls the band variable filter 8 after switching the frequency division number of the variable frequency divider 2. The present invention includes a bandwidth control means for narrowing the passband width of the transmitter.

This frequency synthesizer operates as a normal phase-locked loop in steady state. That is, voltage controlled oscillator 1
, a signal having the same stability as the output signal of the reference oscillator 3 is obtained at a frequency corresponding to the frequency division number N set in the variable frequency divider 2.

However, the control voltage v1 of the voltage controlled oscillator 10 is the sum of the output voltage of the loop filter 5 and the output voltage of the digital-to-analog converter 6. Therefore, frequency F+
Assuming that the loop filter 5 is oscillating, the loop filter 5 performs charging and discharging around a voltage value VL obtained by subtracting the output voltage VIVL of the digital-to-analog converter 6 from the control voltage VI of the voltage-controlled oscillator 1. At this time, data D1 is inputted to the digital-to-analog converter 6 from the control circuit 9. Furthermore, the variable band filter 8 connected to the output side of the digital-to-analog converter 6 has a narrow passband, and suppresses the noise generated in the digital-to-analog converter 6 so as not to transmit it to the voltage-controlled oscillator 1. do. The passband width at this time is assumed to be W2.

Next, the case of switching from frequency F1 to frequency F2 will be described. In frequency switching, the frequency division number of the variable frequency divider 2 is changed, the input data of the digital-to-analog converter 6 is changed, and the band of the variable band filter 8 is changed at the same time. These changes are performed under the control of the control circuit 9.

The frequency division number of the variable frequency divider 2 is changed from the frequency division number N1 corresponding to the frequency F1 to the frequency division number N2 corresponding to the frequency F2. Regarding the input data of the digital-to-analog converter 6, if the control voltage of the voltage controlled oscillator 1 corresponding to the frequency F2 is V2, then the frequency F+ (voltage VI
Data D1 corresponding to VL) is changed to data D2 corresponding to V, -V alliance.

At the same time as changing the frequency division number and changing the data of the digital-to-analog converter 6, the passband width of the variable band filter 8 is set to Wl, which is wider than W2.

As a result, the output voltage of the digital-to-analog converter 6 is transmitted to the adder 7 at high speed, and the control voltage of the voltage controlled oscillator 1 is changed to V2 at high speed. This allows high-speed frequency switching.

After switching the frequency, the passband width of the variable band filter 8 is reset to W2 again. This suppresses the noise generated in the digital-to-analog converter 6 and prevents deterioration of the noise characteristics in the output of the voltage controlled oscillator l.

Therefore, the frequency can be switched at high speed without deteriorating the noise characteristics of the voltage controlled oscillator 1 in a steady state.

FIG. 2 shows an example of a specific circuit of the variable band filter 8. In FIG. This variable band filter 8 is composed of a voltage controlled resistor 81 whose resistance value changes depending on a control voltage, and a capacitor 82.

FIG. 3 shows an example of the voltage controlled resistor 81. As the voltage controlled resistor 81, a field effect transistor whose resistance value between the source and drain changes depending on the voltage applied to the gate can be used. When the resistance value is large, the pass band width becomes narrow, and when the resistance value is small, the pass band width becomes wide.

FIG. 4 is a block diagram of a frequency synthesizer according to a second embodiment of the present invention.

This embodiment includes a variable band filter 8 and a loop filter 5.
This embodiment differs from the first embodiment in that the output of the variable band filter 8 is directly connected to the loop filter 5 in order to add the voltages. The operation in this case is the same as in the first embodiment.

FIG. 5 is a block diagram of a frequency synthesizer according to a third embodiment of the present invention.

This embodiment differs from the first embodiment in that a variable band filter 8 is connected between the adder 7 and the voltage controlled oscillator l. However, the behavior is the same.

In this embodiment as well, the band of the variable band filter 8 is changed at the time of frequency switching. Thereby, frequency switching can be performed at high speed without deteriorating the noise characteristics of the voltage controlled oscillator 1 in a steady state.

FIG. 6 is a block diagram of a frequency synthesizer according to a fourth embodiment of the present invention.

In this embodiment, the digital-to-analog converter 6 is connected to a capacitor in the loop filter 5, and the control voltage from the digital-to-analog converter 6 is stored in this capacitor, and then the digital-to-analog converter 6 is disconnected. , a switch 10 is provided between the digital-to-analog converter 6 and the capacitor.

In steady state, the control circuit 9 opens the switch 10 and disconnects the digital-to-analog converter 6 from the loop filter 5. Therefore, at this time, the normal phase-locked loop operates, and the voltage-controlled oscillator 1 outputs a signal with the same stability as the output signal of the reference oscillator 3 at the frequency division number N set in the variable frequency divider 2. Obtained at the frequency corresponding to.

Next, the case of switching from frequency F1 to frequency F2 will be described.

First, before switching the frequency, the voltage V2 across the capacitor in the loop filter 5, which will be in a steady state after the frequency switching, is set in advance in the digital-to-analog converter 6. Next, in order to perform frequency switching, the control circuit 9 sets the frequency division number N2 corresponding to the frequency F2 to which the frequency is to be switched in the variable frequency divider 2, and at the same time, the switch 10
, the output voltage V of the digital-to-analog converter 6
2 is applied across the capacitor in the loop filter 5. As a result, the capacitor is rapidly charged, and the frequency of the voltage controlled oscillator I is quickly switched to the frequency F2. Subsequently, after charging of the capacitor is completed, switch 10 is turned on.
is opened to cut off the output of the digital-to-analog converter 6 from the loop filter 6.

The time from when the switch 10 is closed to when it is reopened is determined by measuring the charging time of the capacitor in advance and using that value. Furthermore, if the charging time of the capacitor is long, the charging time can be shortened by controlling the output waveform of the digital-to-analog converter 6 to have an overshoot waveform.

The output of the digital-to-analog converter 6 is connected to the switch 10
It is directly connected to the capacitor of the loop filter 5 via. Therefore, if the output impedance of the digital-to-analog converter 6 is sufficiently small, the capacitor can be charged very quickly. Further, since the digital-to-analog converter 6 is cut off from the loop filter 5 after the capacitor is charged, the noise generated from the digital-to-analog converter 6 is also cut off, and does not affect the oscillation signal of the voltage-controlled oscillator 1. There is no. Therefore, frequency switching can be performed at high speed without deteriorating the noise characteristics of the oscillation signal of the voltage controlled oscillator 1.

As the switch 10, a digital-to-analog converter 6 is used.
A variable resistor can also be used since the circuit blocks signals from the In addition, when using a digital-to-analog converter 6 whose output impedance is high to the extent that it does not affect the characteristics of the phase-locked loop when the power is turned off, the switch 10 can be omitted and the digital-to-analog conversion A switch can also be provided on the power supply side of the device 6.

Further, although an example in which a capacitor is used as the voltage holding means has been described, the present invention can be similarly implemented using other voltage holding circuits, such as a peak value holding circuit.

FIG. 7 is a block diagram of a frequency synthesizer according to a fifth embodiment of the present invention. In this embodiment, a variable frequency divider 11 with reset is used in place of the variable frequency divider 2 in the fourth embodiment.

Frequency switching in this embodiment is performed by closing the switch 10 and quickly setting the set voltage V2 corresponding to the switching destination frequency F2 output by the digital-to-analog converter 6 to the loop filter 5, as in the third embodiment. In particular, it is done by Immediately after setting the control voltage to the loop filter 5 at high speed, the switch 10 is opened to disconnect the digital-to-analog converter 6, and at the same time or just before that, the rising or falling edge of the reference signal from the reference oscillator 3 is detected. , a very short-term reset is applied to the variable frequency divider 11 with reset. By this operation, immediately after opening the switch 10, the frequency is set to the switching destination value, and moreover, the phases of the two manual inputs of the phase comparator 4 are brought into a state of matching. Therefore, the phase-locked loop quickly becomes stable.

Therefore, after the frequency switching operation, a stable oscillation signal can be obtained without frequency fluctuation due to phase error and without deterioration of noise characteristics.

The variable frequency divider 11 with reset can also be used in place of the variable frequency divider 2 of the first to third embodiments.

In that case, when switching the frequency, immediately after changing the output voltage of the digital-to-analog converter 6 to the set voltage V2 corresponding to the switching destination frequency F2, the rising or falling edge of the reference signal from the reference oscillator 3 is Detect and
A very short-term reset is applied to the variable frequency divider 11 with reset. This sets the frequency to the value you want to switch to,
Moreover, the phases of the two inputs of the phase comparator 4 match.

Therefore, the phase-locked loop quickly becomes stable.

Furthermore, immediately after switching the frequency, the band variable filter 8
By narrowing the band, a stable oscillation signal can be obtained without frequency fluctuations due to phase errors occurring after the frequency switching operation and without deterioration of noise characteristics.

In the above embodiment, the reference signal is supplied from the reference oscillator 3, but the present invention can be implemented in the same way even if the reference signal is supplied from outside via wireless or the like.

〔Effect of the invention〕

As explained above, the frequency synthesizer of the present invention has
The digital-to-analog converter, which degrades the noise characteristics of the voltage-controlled oscillator, is connected to a noise-suppressing filter or disconnected from the phase-locked loop outside of frequency switching operations. Therefore, frequency switching can be performed at high speed, and deterioration of the noise characteristics of the voltage controlled oscillator during steady state can be prevented.

The present invention is particularly effective when used in a wireless communication device that switches between and uses a plurality of wireless channels. In such a wireless communication device, it is desirable to detect an unused wireless channel at high speed, and to switch wireless channels without interruption during communication. By using the frequency synthesizer of the present invention as a local oscillator in such a wireless communication device, a stable local oscillation frequency can be obtained, wireless channels can be switched at high speed, and empty channel detection and uninterrupted channel switching can be performed. It is easy to execute and has the effect of increasing the functionality and performance of the device.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a frequency synthesizer according to a first embodiment of the present invention. FIG. 2 is a circuit diagram showing a specific example of a variable band filter. FIG. 3 is a circuit diagram showing an example of a voltage controlled resistor. FIG. 4 is a block diagram of a frequency synthesizer according to a second embodiment of the present invention. FIG. 5 is a block diagram of a frequency synthesizer according to a third embodiment of the present invention. FIG. 6 is a block diagram of a frequency synthesizer according to a fourth embodiment of the present invention. FIG. 7 is a block diagram of a frequency synthesizer according to a fifth embodiment of the present invention. FIG. 8 is a block diagram showing a first conventional example. FIG. 9 is a block diagram showing a second conventional example. 1... Voltage controlled oscillator, 2... Variable frequency divider, 3...
・Reference oscillator, 4... Phase comparator, 5... Loop filter, 6... Digital/analog converter, 7...
- Adder, 8... Variable band filter, 9... Control circuit, 10... Switch, 11... Variable frequency divider with reset, 81... Voltage control resistor, 82... Capacitor . Patent Applicant Nippon Telegraph and Telephone Corporation Agent Patent Attorney Ide Nao Takashi Pi Diagram of Summer 5th Shoulder 2 Bushes Example of Fan 4 Mouth Helmet! For example, 1g of iris 6 times

Claims (1)

[Claims] 1. A voltage controlled oscillator, a variable frequency divider that divides the output of the voltage controlled oscillator, and a phase comparator that compares the output phase of the variable frequency divider with the phase of a reference signal; a loop filter that smoothes the output of the phase comparator and supplies it to the voltage-controlled oscillator; and an oscillation frequency control means that controls the oscillation frequency of the voltage-controlled oscillator by switching the division number of the variable frequency divider. The oscillation frequency control means supplies the voltage controlled oscillator with a control voltage corresponding to the switched frequency division number in synchronization with the switching of the frequency division number of the variable frequency divider, and increases the oscillation frequency at high speed. In a frequency synthesizer including a voltage supply means for changing, the voltage supply means includes a variable band filter having a variable pass band width, and the oscillation frequency control means narrows the pass band width of the variable band filter after the switching. A frequency synthesizer characterized in that it includes a bandwidth control means for controlling a frequency. 2. A voltage controlled oscillator, a variable frequency divider that divides the output of this voltage controlled oscillator, a phase comparator that compares the output phase of this variable frequency divider with the phase of a reference signal, and an output of this phase comparator. and an oscillation frequency control means for controlling the oscillation frequency of the voltage control oscillator by switching the frequency division number of the variable frequency divider, The means includes voltage supply means for supplying a control voltage corresponding to the switched frequency division number to the voltage controlled oscillator in synchronization with the switching of the frequency division number of the variable frequency divider, and for changing the oscillation frequency at high speed. In the frequency synthesizer, the voltage supply means is connected to the voltage holding means in the loop filter, and the oscillation frequency control means supplies the voltage after the control voltage from the voltage supply means is stored in the voltage holding means. A frequency synthesizer comprising means for separating the means.