JPH0621981A - Radio transmitter and receiver - Google Patents

Abstract

PURPOSE:To perform demodulation without fail at the side of reception even though a transmission signal has a long-cycle or discrete pulse by mixing the oscillation circuit of a PLL circuit and a VCXO oscillation signal at the time of transmission. CONSTITUTION:When a master unit performs transmission by means of a 1st channel, a PLL in a transmission circuit 3 and a VCO 31a of a circuit 31 perform oscillation by 449.8125MHz. A 20MHz signal oscillated by a VCXO 32 changes by + or -1.5KHz according to the digital signal being transmitted. When the oscillation signal from the PLL circuit 31 and the oscillation signal from the VCXO 32 are mixed by a mixing circuit 33, a transmission signal being the frequency of 429.8125MHz of the transmission frequency which is the 1st channel of the master unit and displacing by + or -1.5KHz according to the digital signal is outputted. Therefore, the oscillation frequency of the VCO 31a is kept at the constant value for each channel by a VCO control circuit 31b. As the transmission signal outputted from the mixing circuit 33 does not accept the frequency correction by the PLL circuit 31, the change of + or -1.5KHz modulated by the digital signal is kept maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless transmission / reception equipment used for a wireless transmission device of digital data.

[0002]

2. Description of the Related Art A radio transmission / reception facility (TRX) for transmitting digital data is used, for example, when a computer wirelessly transmits data to a printer. Such wireless transmission / reception equipment for digital data transmission has a plurality of transmission / reception channels. For example, in the first channel, 429.8125 MHz is allocated as the transmission frequency of the master unit and the reception frequency of the slave unit, and the reception of the master unit is performed. 449.7125 MHz is assigned as the frequency and the transmission frequency of the slave unit. Further, frequencies higher than this by 12.5 kHz are assigned to the second and subsequent channels, respectively.

FIG. 2 shows a conventional transmission / reception circuit in the radio transmission / reception facility for digital data transmission.

The transmission circuit 3 includes a PLL [phase locked l
oop] circuit 31 is provided. The PLL circuit 31 is
VCO [voltage controlled oscillator] 31a and VC
A circuit that is configured by an O control circuit 31b, compares the oscillation frequency of the VCO 31a with a reference frequency in the phase comparator of the VCO control circuit 31b, and feeds back the comparison result to the VCO 31a to obtain a stable oscillation frequency. is there. Further, this PLL circuit 31 has a VC
Since the oscillation frequency can be changed stepwise by changing the frequency division ratio in the O control circuit 31b, the transmission carrier signals of the respective channels differing by 12.5 kHz are obtained.

The digital signal to be transmitted is P
The frequency of the carrier signal for transmission, which is sent to the control input of the VCO 31a in the LL circuit 31 and is directly shifted by the FSK [frequency shift keying] method, is displaced within a range of ± 1.5 kHz, for example. Therefore, the PLL circuit 31
Outputs a transmission signal obtained by modulating the transmission carrier signal for each channel with a digital signal. Then, this transmission signal is amplified by the high frequency amplification circuit 34 and output from the transmission circuit 3.

The transmission signal output from the transmission circuit 3 is sent to the antenna 1 via the duplexer 2 and is transmitted as a radio wave from here. The received signal received by the antenna 1 is sent to the receiving circuit 4 via the duplexer 2 and demodulated into the original digital signal here.

[0007]

However, the above-mentioned PLL is used.
The circuit 31 controls the VCO 31a so as to maintain the oscillation frequency determined by the setting of the frequency division ratio in the VCO control circuit 31b as much as possible. However, if the direct FSK modulation is performed, this VC
The oscillation frequency of O31a is slightly displaced in the positive and negative directions according to the digital signal.

Therefore, for example, when a digital signal as shown in FIG. 3 is to be transmitted, the oscillation frequency of the VCO 31a once becomes +1.5 kHz when the digital signal changes from "0" to "1". Although it is displaced, while the digital signal remains "1",
The oscillation frequency gradually increases or decreases by the action of the PLL circuit 31.
The frequency is pulled back to zero. In addition, even if the digital signal changes from "1" to "0", it is temporarily -1.5.
Although the frequency shifts to the frequency of kHz, the oscillation frequency is gradually returned to the frequency of ± 0 while the digital signal maintains the state of "0" thereafter.

Therefore, the conventional radio transmitter / receiver equipment is used when the digital signal to be transmitted is a signal having a relatively long period such as a synchronizing pulse of a television screen, or a signal including other discrete pulses. Increases the time that the digital signal is maintained at the value of "0" or "1",
Since the frequency displacement is almost eliminated by the PLL circuit 31, there is a problem that the digital signal may not be accurately demodulated on the receiving side.

[0010]

According to the present invention, a PLL circuit for obtaining a stable oscillation frequency by comparing the oscillation frequency of a VCO with a reference frequency by a phase comparator and controlling the VCO based on the comparison result, It is characterized by including a transmitting circuit including a VCXO whose oscillation frequency is displaced by a digital signal, and a mixing circuit which mixes the oscillation signal of the PLL circuit and the oscillation signal of the VCXO to obtain a transmission signal of a transmission frequency.

According to the present invention, the oscillation frequency of the VCO is compared with the reference frequency by the phase comparator, and the PLL circuit for obtaining a stable oscillation frequency by controlling the VCO based on the comparison result, and the oscillation frequency by the digital signal An oscillator circuit using a displaced ceramic resonator,
It is characterized in that it has a transmission circuit provided with a mixing circuit for mixing the oscillation signal of the PLL circuit and the oscillation signal of the oscillation circuit using a ceramic resonator to obtain a transmission signal of a transmission frequency.

[0012]

According to the structure of claim 1, the PLL circuit has a VC
The oscillation frequency of O is compared with the reference frequency by the phase comparator, and a stable oscillation frequency is obtained by forming a phase locked loop that controls the VCO based on the comparison result. Then, by appropriately changing the frequency division ratio before comparison with the phase comparator, it is possible to obtain an oscillation signal of an arbitrary frequency within a stepwise limited range. Will be able to change.

The VCXO is one of oscillation circuits which can obtain a stable oscillation frequency by using a crystal oscillator.
The oscillation frequency of the crystal unit can be slightly displaced by changing the circuit constant of the variable capacitance diode (varicap) or the like according to the voltage applied to the control input. Then, the digital signal is applied to the control input of this VCXO to modulate the oscillation signal of the crystal oscillator.

The mixing circuit is a circuit that mixes the oscillation signal of the PLL circuit and the oscillation signal of the VCXO, and thereby obtains a transmission signal having a transmission frequency. Therefore, the oscillation frequency of the PLL circuit is set such that the difference from the transmission frequency of the channel matches the original (unmodulated) oscillation frequency of the VCXO.

As a result, the wireless transmission / reception equipment according to claim 1
The VCXO oscillation signal is temporarily modulated by the digital signal to be transmitted, and then mixed with the oscillation signal of the PLL circuit by the mixing circuit to generate the transmission signal. Therefore, P
In the LL circuit, the oscillation of the frequency corresponding to the transmission frequency of the channel is always maintained, and the transmission signal modulated by the digital signal to be transmitted is not affected by the PLL circuit.

According to the configuration of claim 2, the VCXO of claim 1
Instead of this, an oscillation circuit using a ceramic resonator is used. In this oscillator circuit, a crystal resonator of VCXO is replaced with a ceramic resonator. Therefore, VC
Although not as high as that of XO, a signal having a sufficiently stable oscillation frequency can be modulated by a digital signal, so that the same effect as in the case of claim 1 can be obtained.

[0017]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention and is a block diagram of a transmission / reception circuit in a radio transmission / reception facility. In addition, the same numbers are added to the constituent members having the same functions as those of the conventional example shown in FIG.

In this embodiment, a wireless transmission / reception facility for digital data transmission will be described.

In this wireless transmission / reception facility, digital signals are wirelessly transmitted / received between the master unit and the slave unit via the antenna 1. This antenna 1 is connected to a transmission circuit 3 and a reception circuit 4 via a duplexer 2, respectively. The duplexer 2 sends out the received signal received by the antenna 1 to the receiving circuit 4 without leaking to the transmitting circuit 3 side, and sends the transmitting signal sent from the transmitting circuit 3 to the antenna 1 without leaking to the receiving circuit 4 side. It is a directional filter designed to send out.

The transmission circuit 3 includes a PLL circuit 31 and a VC.
It is composed of an XO 32, a mixing circuit 33, and a high frequency amplifier circuit 34.

The PLL circuit 31 includes a VCO 31a and a VCO.
It is a phase-locked loop formed by the control circuit 31b. The VCO 31a is a voltage-controlled oscillation circuit that can arbitrarily change the oscillation frequency by changing the capacitance of the variable capacitance diode provided in the tuning circuit according to the voltage applied to the control input. When the wireless transmission / reception equipment is the master unit (transmission frequency is 429 MHz
The band) is set so that the oscillation frequency of the VCO 31a is in the 449 MHz band, which is 20 MHz higher than the transmission frequency. The VCO control circuit 31b compares the oscillation frequency of a crystal oscillation circuit (not shown) with the oscillation frequency of the VCO 31a using a phase comparator as a reference frequency, amplifies the low frequency component of the phase difference signal, and feeds it back to the control input of the VCO 31a. The circuit is designed to stabilize the oscillation frequency. Further, the PLL circuit 31 adjusts the division ratio of the oscillation frequency of the VCO 31a and the division ratio of the reference frequency for comparison by the phase comparator by rewriting the internal data, and the oscillation frequency of the VCO 31a is set to 1
It is possible to change channels in 2.5 kHz steps.

The VCXO 32 uses a crystal oscillator 20
This is an oscillating circuit having an oscillating frequency of MHZ, and this oscillating frequency can be displaced within a range of several kHz by changing the capacitance of the variable capacitance diode by the voltage applied to the control input. And
A digital signal for transmission is input to the control input of the VCXO 32, and an oscillation frequency of 20 MHz is ± 1.5 k depending on the value of "0" or "1" of the digital signal.
It is designed to displace only Hz. Therefore, VCXO
32 outputs a signal obtained by modulating the oscillation frequency of the crystal unit with a digital signal by the FSK method.

The mixing circuit 33 is a circuit for mixing the oscillation signal from the PLL circuit 31 and the oscillation signal from the VCXO 32. That is, the mixing circuit 33 is the PLL circuit 3
12.5 kHz different for each channel from 1 44
The difference frequency between the 9 MHz band oscillation signal and the 20 MHz oscillation signal modulated by the digital signal from the VCXO 32 is taken to obtain the transmission frequency of the master unit.
A 9 MHz band transmission signal can be output, and this transmission signal is also modulated by a digital signal by the FSK method.

The high frequency amplifier circuit 34 is the mixing circuit 33.
It is a circuit that amplifies the transmission signal output by
It also has a band-pass filter that passes only high-frequency signals in the 9 MHz band.

The receiving circuit 4 is a circuit for demodulating a received signal received by the antenna 1 into an original digital signal.

With the above configuration, when the base unit performs transmission using the first channel, for example, the PL in the transmission circuit 3 is
The VCO 31a of the L circuit 31 oscillates at 449.8125 MHz. Also, the signal of 20 MHz oscillated by the VCXO32 is
It is displaced by ± 1.5 kHz depending on the transmitted digital signal. When the oscillation signal from the PLL circuit 31 and the oscillation signal from the VCXO 32 are mixed by the mixing circuit 33, 429.8125 which is the transmission frequency of the first channel of the parent device.
Frequency of MHZ, ± 1.
A transmission signal that is displaced by 5 kHz is output.

Therefore, the VCO 3 in the PLL circuit 31
The oscillation frequency of 1a is maintained at a constant value for each channel by the VCO control circuit 31b without being affected by the digital signal to be transmitted. In addition, the mixing circuit 33
The transmission signal output from is not subjected to frequency correction by the PLL circuit 31, and is therefore modulated by a digital signal ±.
The displacement of 1.5 kHz is maintained.

As a result, according to the wireless transmission / reception equipment of this embodiment, even if the frequency to be transmitted has a long cycle or has discrete pulses, the frequency corresponding to this digital signal The displacement is maintained, and the problem that the receiving side cannot accurately demodulate is solved.

It should be noted that in the present embodiment, V of crystal oscillator is used.
The CXO 32 was used to modulate the digital signal, but if the accuracy of the oscillation frequency is acceptable, it is also possible to use an oscillation circuit in which this crystal oscillator is replaced with a ceramic resonator.

[0031]

As is apparent from the above description, in the radio transmitting / receiving equipment of the present invention, since the frequency of the transmission signal modulated by the digital signal is not modified by the PLL circuit, this digital signal is transmitted. Even if it has a long cycle or has a discrete pulse, it is possible to reliably demodulate this at the receiving side.

[Brief description of drawings]

FIG. 1 is a block diagram of a transmission / reception circuit in a wireless transmission / reception facility according to an embodiment of the present invention.

FIG. 2 is a block diagram of a transmission / reception circuit in a wireless transmission / reception facility, showing a conventional example.

FIG. 3 shows a conventional example and is a time chart showing a relationship between a digital signal to be transmitted and an oscillation frequency of a VCO.

[Explanation of symbols]

 31 PLL circuit 31a VCO 31b VCO control circuit 32 VCXO 33 mixed circuit

Claims (2)

[Claims] 1. A PLL circuit for obtaining a stable oscillation frequency by comparing the oscillation frequency of the VCO with a reference frequency by a phase comparator and controlling the VCO based on the comparison result, and the oscillation frequency is displaced by a digital signal. VCX
A wireless transmission / reception facility comprising: a transmission circuit including O and a mixing circuit that mixes an oscillation signal of a PLL circuit and an oscillation signal of a VCXO to obtain a transmission signal of a transmission frequency. 2. A PLL circuit which obtains a stable oscillation frequency by comparing the oscillation frequency of the VCO with a reference frequency by a phase comparator and controlling the VCO based on the comparison result, and the oscillation frequency is displaced by a digital signal. And a mixing circuit that mixes the oscillation signal of the PLL circuit and the oscillation signal of the oscillation circuit using the ceramic resonator to obtain a transmission signal of a transmission frequency. Wireless transmission and reception equipment.