JPH0732366B2 - Wireless transmitter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a wireless transmitter of the type that directly uses the output of a frequency synthesizer as a transmission wave, and more specifically, it occurs when the power of a transmission power amplifier is turned on. The present invention relates to a wireless transmitter that suppresses drift of transmission frequency as much as possible.

[Prior Art] In recent years, a frequency synthesizer using a PLL (phase-locked loop) circuit has become possible to be constructed at low cost, and as a result, it is common to use a frequency synthesizer dedicated to transmission even in a small radio transmitter. Has become.

In other words, this type of wireless transmitter makes the oscillation frequency of the voltage-controlled oscillator (hereinafter sometimes abbreviated as "VCO") used in the frequency synthesizer the same as the transmission wave, and also directly modulates the VCO It is possible to easily eliminate transmission spurs other than harmonics compared to a radio transmitter using a multiplication method, a mixer method, etc. Have contributed.

FIG. 2 is a block diagram showing a conventional wireless transmitter using a frequency synthesizer.

The frequency synthesizer 10 includes a reference oscillator 1, a fixed frequency divider 2,
Phase comparator 3, low frequency signal modulator 4, low pass filter 5, VO
It is composed of C6, prescaler 8 and variable frequency divider 7.

The transmission wave transmitted from the VCO 6 is amplified by the transmission power amplification section 20 including the pre-driver amplifier 21 and the power amplifier 22 and transmitted from the output terminal 24.

Here, since it takes time for the frequency synthesizer 10 to lock after power is turned on and the frequency becomes stable, the frequency synthesizer 10 is always in a state in which the power is turned on. Therefore, the transmission control is performed by turning on and off the power of the transmission power amplification unit 20. That is, power is supplied to the transmission power amplification unit 20 from the power supply terminal 25 via the switch 23, and the switch 23 is turned on / off by a control signal from the terminal 26 to turn on / off the switch.

The output of the frequency synthesizer 10 is the transmission power amplifier.
In order to minimize the change in the load impedance of VOC6 that occurs when the power of 20 is turned on and off, buffer 15
It was input to the transmission power amplification unit 20 via.

[Problems to be solved] In the above-described conventional wireless transmitter, the load state of the VCO changes abruptly at the moment when the transmission power amplification unit 20 is turned on for transmission, and thus the frequency of the frequency synthesizer slightly drifts. To do.

The state of this drift is a unique pattern due to the loop characteristic of the frequency synthesizer 10 (power is turned on to the transmission power amplification unit 20, the stable state of the transmission power amplification unit 20 is rapidly changed, and the transmission power amplification unit 20 is changed from the VCO 6 to the transmission power amplification unit 20. The load impedance as seen suddenly changes and the PLL of the frequency synthesizer 10
The loop shows a transient state pattern when it tries to follow this change), and sometimes the drift frequency greatly deviates from the original frequency or the drift time becomes very long.

If the frequency drift is large, the transmitted wave deviates from its own band and causes other interference as a transmission spurious. In addition, in recent years, when a data signal is often transmitted at the beginning of transmission, it is necessary to reliably transmit this data signal in the shortest possible time. Therefore, frequency drift requires that the detuning be as small as possible and the time be as short as possible. .

As a means for solving this problem, it is conceivable to increase the number of stages of buffers connected to the VCO so as to minimize the change in load impedance of the VCO due to power-on of the transmission power amplifier. However, when the number of the buffer stages is increased, the space for the buffer and the power consumption are increased accordingly, which leads to an increase in the size of the device and a decrease in economical efficiency, which has been a problem.

The present invention has been made in consideration of the above problems,
It is an object of the present invention to provide a wireless transmitter that can reduce a change in load impedance of a VCO in a frequency synthesizer and can reduce the size of the device and maintain low power consumption.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a voltage-controlled oscillator capable of being externally modulated, a phase comparator, and a loop filter provided between the voltage-controlled oscillator and the phase comparator. , A PLL frequency comprising a variable frequency divider provided in a feedback line from the output side of the voltage controlled oscillator to the phase comparator, and a reference oscillator for transmitting a reference signal to the phase comparator via a fixed frequency divider. A synthesizer,
In a radio transmitter including a transmission power amplifier that amplifies the output of the voltage controlled oscillator in the PLL frequency synthesizer to generate a transmission wave, for opening and closing a phase locked loop between the phase comparator and the loop filter. Switch is provided, a first clock gate is provided between the voltage controlled oscillator and the variable frequency divider, a second clock gate is provided between the reference oscillator and the fixed frequency divider, and the switch is provided. And the first and second clock gates,
The transmission power amplifier is turned off immediately before the power is turned on, and is connected after the transmission power amplifier is stabilized for a predetermined time after the power is turned on.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a wireless transmitter according to this embodiment. In FIG. 1, the same parts as those in FIG. 2 shown above are designated by the same reference numerals.

The radio transmitter shown in FIG. 1 is a frequency synthesizer 10,
The transmission power amplification unit 20 and the control unit 30 are included.

Frequency synthesizer 10 is a voltage controlled oscillator (VCO) 6,
Based on a PLL circuit including a phase comparator 3 and a low-pass filter (loop filter) 5, a reference oscillator 1 is provided on the input side of the phase comparator 3 via a fixed frequency divider 2, and a prescaler 8 and It has a general configuration in which a variable frequency divider 7 is provided. The VCO 6 can be externally modulated by the low frequency modulator 4. In the figure, 9 is a modulation terminal.

Further, the wireless transmitter according to the present embodiment has the following configuration in addition to the above general configuration of the frequency synthesizer 10. That is, between the phase comparator 3 and the low-pass filter 5, an analog switch that opens and closes the connection therebetween.
11 is provided. In addition, the prescaler 8 and the variable frequency divider 7
The signal fed back is turned ON (conduction) or
There is a first clock gate 12 that turns off (shuts off),
Transmit the oscillation signal between the reference oscillator 1 and the fixed frequency divider 2.
Second clock gate 1 that turns on (conducts) or turns off (shuts off)
3 is provided.

The transmission power amplification unit 20 includes a pre-driver amplifier 21 and a power amplifier 22, and amplifies the transmission wave transmitted from the VCO 6 of the frequency synthesizer 10 and transmits it to the transmission output terminal 24.

Power is constantly supplied to the frequency synthesizer 10. Further, the transmission power amplification unit 20 is supplied with an output from a power supply terminal 25 via a power supply switch 23.

The control unit 30 controls ON / OFF of the power switch 23 to operate or stop the transmission power amplification unit 20. Further, in connection with the power-on operation of the transmission power amplifier 20, ON / OFF control of the analog switch 11, the first and second clock gates 12 and 13 in the frequency synthesizer 10 is performed.

That is, the power switch 23 is turned on and the transmission power amplifier 20
Just before turning on the power to the switch 11,
The clock gates 12 and 13 are turned off (interrupted) to open the PLL loop of the frequency synthesizer 10. This allows
Even if the stable state of the transmission power amplification unit 20 suddenly changes when the transmission power amplification unit 20 is powered on, the frequency synthesizer 10
Need not follow this state change.

Also, the switch 11, the clock gates 12 and 13 are turned on (conduction) after a lapse of a predetermined time after the power of the transmission power amplifier 20 is turned on.
The PLL loop of the frequency synthesizer 10 is controlled to be a closed loop. As a result, the transmission power amplifier 20
After the power was turned on for a certain period of time, the transmission power amplifier 20 became stable, and then the PLL of the frequency synthesizer 10
The loop becomes a closed loop.

For example, the turning-off time may be set 1 msec before the power is turned on, and the turning-on time may be set 5 msec after the power is turned on. However, it is not limited to this.

Thus, the PLL loop of frequency synthesizer 10
It is possible to shift to the next stable state without passing through a transient state accompanied by a sudden change when the power of the transmission power amplification unit 20 is turned on.

As described above, when the analog switch 11 is turned off immediately before the power supply to the transmission power amplification unit 20 is turned on, the VCO 6 becomes free run due to the voltage charged by the low pass filter 5. Therefore, the frequency synthesizer 10 operates in open loop, and the change in the load impedance of the VCO 6 becomes very small. Further, at this time, since the first and second clock gates 12 and 13 are also turned off, the fixed frequency divider 2,
The phase comparator 3 and the variable frequency divider 7 maintain the same state as when the frequency synthesizer 10 is in the synchronization state.

Next, after a lapse of a predetermined time from turning on the power, the analog switch 1
1, when the second clock gate 12, 13 is turned on, VCO6
It is in the free-run state due to the voltage charged by the low-pass filter 5, and the transmission power amplification unit 20
The oscillation frequency changes slightly under the influence of the load impedance change caused by turning on the power. However, the changing frequency is very small because there is no specific pattern because it does not relate to the loop characteristic of the frequency synthesizer 10, and therefore the synchronizing state is restored again in an extremely short time.

Also, the switch 11, the first and second clock gates 12 and 13 are
Since it can be handled digitally at a low frequency part, CMOS LSI can be used, which enables downsizing and low power consumption.

[Effects of the Invention] As described above, according to the present invention, the change in the load impedance of the VCO in the frequency synthesizer can be made small, so that there is an effect that the synchronization state is restored again in an extremely short time and the accuracy can be improved. Further, since small components such as CMOS LSI can be used for the switches and the first and second clock gates, it is possible to downsize the device and maintain low power consumption.

[Brief description of drawings]

FIG. 1 is a block diagram showing a wireless transmitter according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional example. 1: Reference oscillator, 2: Fixed frequency divider 3: Phase comparator, 4: Low frequency modulator 5: Low pass filter, 6: Voltage controlled oscillator 7: Variable frequency divider, 8: Prescaler 9: Modulation element, 11: Analog switch 12: First clock gate 13: Second clock gate 20: Transmission power amplification section 21: Pre-driver amplifier 22: Power amplifier, 23: Power switch 24: Transmission output terminal, 25: Power supply terminal 30: Control section

Claims (1)

[Claims] 1. A voltage-controlled oscillator capable of being externally modulated, a phase comparator, a loop filter provided between the voltage-controlled oscillator and the phase comparator, and the phase comparison from the output side of the voltage-controlled oscillator. Frequency synthesizer comprising a variable frequency divider provided in the feedback line to the frequency divider, and a reference oscillator for transmitting a reference signal to the phase comparator via a fixed frequency divider, and the voltage controlled oscillator in this PLL frequency synthesizer In a wireless transmitter including a transmission power amplifier that amplifies the output of the device 1 to a transmission wave, a switch for opening and closing a phase locked loop is provided between the phase comparator and the loop filter, and the voltage controlled oscillator A first clock gate between the variable frequency divider and the variable frequency divider, and a second clock gate between the reference oscillator and the fixed frequency divider. And disconnecting the switch and the first and second clock gates immediately before turning on the power of the transmission power amplification unit, and connecting the transmission power amplification unit after the transmission power amplification unit has stabilized for a predetermined time. A wireless transmitter comprising a control unit for controlling the operation.