JP2000324000A - Oscillator for transmission, and transmitter and receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease used components to reduce the size and to attain small power consumption by enabling distortionless frequency modulation without sacrificing the stability and noise of an oscillation output signal, using the oscillator for transmission even as a 2nd local oscillator for reception, and eliminating the need for a frequency divider. SOLUTION: A 1st low-pass filter 21 is connected to one end of a varactor diode 20 for frequency variation and a 2nd low-pass filter 23 is connected to one end of a varactor diode 22 for modulation; and the other-end sides of the varactor diodes 20 and 22 are grounded through a common resistance 24; while a voltage for frequency control is supplied to one end of the varactor diode 20 through the low-pass filter 21, a modulation signal is supplied to one end of the varactor diode 22 for modulation through the 2nd low-pass filter 23, thereby outputting a frequency-modulated oscillation signal. The time constant of the 2nd low-pass filter 23 is set much shorter than that of the 1st low-pass filter 21 so that the response speed of the modulating signal does not decrease.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission oscillator for modulating the frequency by using a phase-controlled voltage-controlled oscillator, and a transmitter / receiver having the transmission oscillator for alternately transmitting and receiving signals of the same frequency in a time-division manner. About.

[0002]

2. Description of the Related Art A transmission / reception method in which transmission / reception using signals of the same frequency is performed in a time-division manner is generally used in a wireless telephone device or the like, and a so-called wireless LAN device for wirelessly connecting a computer device and a peripheral device. It is also used in the field. Here, the switching time between transmission and reception is set to be sufficiently long in a wireless telephone device that handles voice signals, but is set to be short from several μs to several tens of μs in a wireless LAN device or wireless telephone device compatible with digitization. Increases transmission efficiency. On the other hand, the oscillator included in the transmission / reception unit employs a phase lock (PLL) technology to increase the number of channels at a stable frequency, but the frequency and level of the phase-locked oscillator fluctuate until it starts up and the operation becomes stable. Therefore, the oscillators of the transmission unit and the reception unit are operated continuously, and the transmission and reception are switched by switching the circuit parts capable of high-speed activation except the oscillator. At this time, if the local oscillator of the transmission / reception unit is shared by one oscillator, there is no deviation in the transmission / reception frequency and the frequency adjustment is easy, but this also makes the intermediate frequency of the intermediate frequency amplification stage of the transmission / reception unit the same frequency. If the phase-locked oscillator is operated continuously, the signal generated in the transmission unit during reception jumps into the intermediate frequency amplification stage of the reception stage, causing problems such as suppression of reception sensitivity. For this reason, the transmission unit and the reception unit must be strictly electromagnetically shielded, but if the frequency is high, it cannot be sufficiently shielded.

A transceiver which solves this problem is disclosed in US Pat. No. 5,276,915 (prior art 1). Hereinafter, a conventional transceiver similar to the transceiver disclosed in the above prior art will be described with reference to FIG. In the figure, 1 is a transmitting / receiving antenna, 2 is a receiving unit, 3 is a transmitting unit, and 4 is a switch for switching the antenna 1 between the receiving unit 2 and the transmitting unit 3. Reference numeral 5 denotes a high-frequency amplifier for amplifying a signal received by the antenna 1 in the receiver 2, and 6 mixes the output of the high-frequency amplifier 5 and the oscillation output of the local oscillator 7 to generate a signal of the first reception intermediate frequency. A first receiving mixer 8 for generating the signal, a receiving intermediate frequency amplifying stage 8 for amplifying an output signal of the receiving mixer 6, and 9 mixing the first receiving intermediate frequency signal and the output signal of the second receiving local oscillator 10. And a second reception mixing section for generating a signal of a second reception intermediate frequency. A predetermined circuit is further connected to the subsequent stage of the second reception mixing section 9, but is not shown. 11 is the first reception intermediate frequency 2
A transmission oscillator that oscillates at a double frequency and, although not shown, is connected to a modulation circuit to generate a modulated transmission signal. Reference numeral 12 denotes a frequency divider (prescaler) having a frequency division ratio of 1/2.
At the time of transmission, the frequency of the output signal of the transmission oscillator 11 is set to 1 /
The frequency is divided by 2, and the operation stops when receiving. 13 is a frequency divider 1
A transmission intermediate frequency amplification stage for amplifying the output signal of 0, a transmission mixing unit 14 for mixing the output of the transmission intermediate frequency amplification stage 13 and the oscillation output of the local oscillator 7 to generate a transmission signal, and 15 a transmission mixing unit 14 Out of the output signals, a band-pass filter that passes a signal of the transmission frequency, and 16 denotes a power amplification unit that power-amplifies the output signal of the band-pass filter 15 and supplies the signal to the switch 4. In this transceiver, since the frequency of the transmitting oscillator 11 is different from the frequency of the receiving intermediate frequency amplifying stage 8, even if the transmitting oscillator 11 is operated continuously, no reception disturbance occurs. Therefore, all the oscillators 7, 10, 11 of the receiving unit 2 and the transmitting unit 3 can be operated continuously regardless of transmission / reception. Can be switched at high speed.

In the specification of the prior art 1, the local oscillator 7 whose oscillation frequency is greatly varied is modulated.
In frequency modulation, there is an adverse effect that when the oscillation frequency changes, the frequency shift amount also changes. On the other hand, the transmitter / receiver shown in FIG.
, So that the frequency shift amount does not change even if the transmission output frequency is changed. Also,
The phase-locked oscillator 11 is supplied with a control voltage through a low-pass filter to the variable capacitance element. In order to keep the oscillation output frequency highly stable and to reduce noise, the time constant of the low-pass filter is Set to a large value. By the way, in order to apply frequency modulation with a large shift amount to a high-speed signal having a transmission speed exceeding 1 Mbps, a high-speed, large-amplitude modulation signal must be given to the variable capacitance element.

[0005]

However, the response speed of the signal at the end of the variable capacitance element is limited by the time constant of the low-pass filter, and the level of the modulated signal also decreases. Therefore, if the time constant of the low-pass filter is changed so as to improve the modulation characteristics, the stability and noise of the oscillation output signal are sacrificed, and both characteristics cannot be improved. In addition, when the signal level applied to the variable capacitance element end increases, the frequency shift amount with respect to the modulation signal level becomes non-linear, causing not only distortion, but also the main voltage supplied to the variable capacitance element so as to maintain the oscillation frequency. The control voltage is disturbed by the modulation signal, so that the center frequency of the oscillation output signal becomes unstable, which also causes a problem that the modulation frequency characteristic deteriorates. In a portable PHS telephone device or the like, the operation time is limited by the capacity of the battery. However, in order to extend the operation time while maintaining small size and light weight, a transceiver with low power consumption has been desired.

[0006]

SUMMARY OF THE INVENTION The present invention has been proposed to solve the above-mentioned problems. (1) In a transmission oscillator according to the present invention, a first low-pass filter is connected to one end of a variable-capacitance element for variable frequency, and a second low-pass filter is connected to one end of a variable-capacitance element for modulation. Further, the other end of each variable capacitance element is grounded via a common resistor, and a voltage for frequency control is supplied to one end of the variable capacitance element for frequency variation via a first low-pass filter and modulated. A modulation signal is supplied to one end of a variable capacitance element for use through a second low-pass filter,
The frequency-modulated oscillation signal is output. By this means, the operating point of each variable capacitance element does not change and the center capacitance does not change. (2) In the transmission oscillator according to the present invention, in the transmission oscillator according to the above item (1), the time constant of the second low-pass filter is set sufficiently shorter than the time constant of the first low-pass filter. Have been. By this means, frequency modulation can be performed without lowering the response speed of the modulated signal that changes at a high speed. (3) In the transmission oscillator according to the present invention, in the transmission oscillator according to the above item (1), a variable DC voltage is supplied to one end of a variable capacitance element for modulation. When the oscillation frequency of the transmitting oscillator is switched by this means, the switching of the frequency can be made faster without being affected by the time constant of the first low-pass filter by simultaneously displacing the DC voltage. (4) The receiver according to the present invention mixes the received signal with the output signal of the first receiving local oscillator to obtain a first receiving intermediate frequency signal, and converts this signal to the output signal of the second receiving local oscillator. A receiving unit configured to obtain a second reception intermediate frequency signal by mixing with a transmission unit that generates a transmission signal by mixing the modulated transmission intermediate frequency signal with an output signal of a transmission local oscillator, The first local oscillator for reception and the local oscillator for transmission are shared by one local oscillator, and the transmission intermediate frequency signal and the first reception intermediate frequency signal are set to the same frequency, so that signals of the same frequency are used. In a transmitter / receiver that alternately performs transmission and reception in a time-division manner, a transmission oscillator that generates a transmission intermediate frequency signal is the transmission transmission oscillator described in the above item (1). (5) In the receiver according to the present invention, in the receiver according to the above item (4), different DC voltages are supplied to one end of the variable capacitance element for modulation at the time of transmission and at the time of reception, and the output of the transmission oscillator is output at the time of reception. A signal is mixed with the first reception intermediate frequency signal, and the frequency of the mixed output is made equal to the frequency of the second reception intermediate frequency signal, thereby forming the second reception local oscillator with the transmission oscillator. It is characterized by having done.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1, the same components as those in FIG. 4 are denoted by the same reference numerals, and redundant description will be omitted. 4 is different from FIG. 4 in that a transmitting oscillator 17, which is a characteristic part of the present invention, is connected to the frequency divider 12 instead of the transmitting oscillator 11 in the transmitting unit 103. The transmission oscillator 17 will be described with reference to FIG. In the drawing, 18 is an oscillation transistor, 19 is an oscillation inductor having one end connected to the base of the transistor 18 at a high frequency, and 20 is a frequency variable whose one end is connected to the other end of the inductor 19 to vary the oscillation frequency. Variable capacitance diode as variable capacitance element, 2
Reference numeral 1 denotes a first low-pass filter that supplies a phase lock control voltage to a connection point between the inductor 19 and the variable capacitance diode 20, and removes a ripple component included in the control voltage.
Reference numeral 22 denotes a variable capacitance diode serving as a frequency modulation variable capacitance element to which a modulation signal is supplied at one end via a second low-pass filter 23.
The other end of 22 is DC grounded via a resistor 24. The transistor 18 is connected to a bias resistor, an oscillation feedback capacitor, and the like, but the description is omitted.
Reference numeral 25 denotes a buffer amplifier for amplifying an oscillation output signal from the oscillation transistor 18, and its output is connected to the frequency divider 12.

The output of the transmitting oscillator 17 is further connected to a 1 / M frequency divider 26, the output of which is connected to one input terminal of a phase comparator 27, and the other input terminal has a reference oscillator oscillating at 1 MHz. The phase lock control voltage generated at the output of the phase comparator 27 is supplied to the first low-pass filter 21. Here, the phase control circuit including the 1 / M frequency divider 26, the phase comparator 27, and the reference oscillator 28 is shared with the phase control circuit of the second receiving local oscillator 10, and
The frequency division ratio of the / M frequency divider is appropriately set according to the oscillation frequency of each of the oscillators 10 and 17 during transmission and reception. The oscillator 17 is 1 /
The constants of the inductor 19 and other related elements are set so as to oscillate at a desired frequency by setting the M frequency divider 26. The cut-off frequency of the first low-pass filter 21 is set to about 20 kHz, and the second low-pass filter 23
Is about 3 for a signal whose cut-off frequency is 1Mbps.
MHz, and the respective time constants of the second low-pass filter 2 are smaller than those of the first low-pass filter 21.
3 is markedly smaller. This transmission oscillator 1
7, the other end of each of the variable capacitance diodes 20 and 23 is connected to a resistor 2
4, the elements 20 and 22 are reverse-biased, no current flows through the resistor 24, and the other end voltage of each of the variable capacitance diodes 20 and 23 is always constant at 0V. The variable capacitance diode 20 has a reverse bias voltage of 1.5 V and a capacitance of about 22 pF, and the modulation variable capacitance diode 23 has a reverse bias voltage of 2.5 V and a capacitance of about 13 pF. And different reverse bias voltages can be set.

With such a circuit configuration, the variable capacitance diodes 20, 2 pass through the low-pass filters 21, 23, respectively.
2 does not affect the reverse bias state of the other variable capacitance diodes, the operating point of each of the variable capacitance diodes 21 and 23 does not fluctuate, and the center capacitance also changes. Does not fluctuate. Therefore, the phase lock control voltage supplied to the frequency setting variable capacitance diode 20 through the first low-pass filter 22 having a large time constant is modulated through the second low-pass filter 24 having a small time constant. The oscillation frequency can be stably maintained without being disturbed by the modulation signal supplied to the variable capacitance diode 23 for high-speed change. Each variable capacitance diode 2
Since the operating points 0 and 22 can be set without being influenced by each other, a low-distortion transmission signal can be generated even if a large-amplitude high-speed modulation signal is supplied to the modulation variable capacitance diode 22.

FIG. 3 shows another embodiment of the present invention. In the figure, the same components as those in FIGS. 1 and 4 are denoted by the same reference numerals, and redundant description will be omitted. The difference from FIGS. 1 and 4 is that
The transmitting unit 203 does not include the frequency divider 12, and the receiving unit 202 shares the transmitting oscillator 17 in place of the second receiving local oscillator 10. Transmitting oscillator 1
Reference numeral 7 in this embodiment makes the reverse bias voltage of the variable capacitance diode 22 for modulation shown in FIG. 2 different between transmission and reception.

This transceiver has the same effect as the transceiver shown in FIG. 1, but further effects will be described below together with the operation of this transceiver. First, at the time of transmission, the transmission oscillator 17 applies the phase lock control voltage to the first low-pass filter 21 and the frequency setting variable capacitance diode 20.
Is reverse-biased, has a capacitance corresponding to this voltage, and oscillates at a predetermined frequency set by the frequency division ratio of the 1 / M frequency divider 26. The reverse bias voltage of the variable capacitance diode 22 for modulation is set by the modulation signal supplied to the second low-pass filter 23, and the capacitance is adjusted by the modulation signal with the capacitance corresponding to this voltage as the center. This changes the frequency of the transmission oscillator 17. Next, at the time of reception, the frequency division ratio of the 1 / M frequency divider 26 is switched so that the frequency of the output signal of the transmission oscillator 17 becomes a predetermined frequency required by the second reception local oscillator. At the same time, the DC voltage supplied to the second low-pass filter 23 is displaced, and the reverse bias voltage of the modulation variable capacitance diode 22 is displaced.

Here, for example, if the transmission intermediate frequency and the first reception intermediate frequency are set to 345 MHz, and the frequency of the second reception intermediate frequency signal, which is the output signal of the second reception mixer 9, is set to 11 MHz, it is necessary. Since the second receiving local oscillation frequency is 345 MHz ± 11 MHz, 356 MHz
Alternatively, the frequency division ratio of the 1 / M frequency divider 26 is set to be 334 MHz. At the same time, while the reverse bias voltage of the frequency setting
The reverse bias voltage of the variable capacitance diode 22 for modulation is set so as to be set to MHz or 334 MHz. That is,
The reverse bias voltage of the modulation variable capacitance diode 22 is compared with the DC voltage at the time of transmission, and the transmission intermediate frequency is 345 MHz.
The voltage is increased to increase the reception local oscillation frequency to 356 MHz, and the voltage is decreased to decrease to 334 MHz.

The modulation variable capacitance diode 22
If the second low-pass filter 23 is not provided and the frequency division ratio of the 1 / M frequency divider 26 is switched, the phase lock voltage which is the output voltage of the phase comparator 27 changes,
This voltage is transmitted to the variable-capacitance diode 20 for frequency setting via the first low-pass filter 21, and its capacitance is changed so as to be controlled to a frequency corresponding to the frequency division ratio. Since the time constant of the pass filter 21 is large, it takes time to switch the frequency, and it takes time for the frequency to stabilize after the switching, so that high-speed transmission and reception cannot be switched.

On the other hand, in the transmitter / receiver shown in FIG. 3, the transmission oscillator 17 passes through the second low-pass filter 23 having a small time constant during reception to receive the modulation variable capacitance diode 2.
2 is set to a predetermined voltage, the capacitance is set so as to oscillate at a frequency close to or very close to the second reception local oscillation frequency, and 1 / M frequency division is performed during transmission. The reverse bias voltage applied to the modulation variable capacitance diode 22 changes at the same time as the switching of the frequency division ratio of the modulator 26, and the capacitance is set so as to oscillate at a frequency equal to or very close to the transmission intermediate frequency. Switching between transmission and reception can be performed in a short time regardless of the time constant of the first low-pass filter 21. In addition, since the transmission oscillator 17 in this embodiment has different oscillation frequencies at the time of transmission and at the time of reception, the frequency divider 12 required to avoid the problem of reception interference due to the output signal of the transmission oscillator at the time of reception. Is unnecessary, and the second receiving local oscillator 10 is not required. Therefore, the number of components used can be reduced, the size can be reduced, and the power consumption can be reduced. Therefore, the present invention can be applied to a portable device driven by a battery. it can.

[0015]

As described above, according to the present invention, it is possible to perform frequency modulation without distortion without sacrificing the stability and noise of the oscillation output signal, and to transmit the oscillation output signal of the transmission oscillator. Can be switched in a short time to change to a frequency corresponding to each of reception and reception. Therefore, the transmission oscillator can be shared as the second reception local oscillator, and a frequency divider is not required. Power can also be used.

[Brief description of the drawings]

FIG. 1 is a block diagram of a transceiver showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a transmission oscillator of the apparatus in FIG. 1;

FIG. 3 is a block diagram showing another embodiment of the present invention.

FIG. 4 is a block diagram showing a conventional example of a transceiver.

[Explanation of symbols]

 2, 202 receiving section 103, 203 transmitting section 7 first receiving local oscillator (transmitting local oscillator) 6 first receiving mixing section 10 second receiving local oscillator 14 transmitting mixing section 17 transmitting oscillator 20 frequency Variable capacitance diode for variable 21 First low-pass filter 22 Variable capacitance diode for modulation 23 Second low-pass filter 24 Resistance

Claims (9)

[Claims] A first capacitor is provided at one end of a variable capacitance element for changing a frequency.
And a second low-pass filter is connected to one end of the variable capacitance element for modulation, and the other end of each variable capacitance element is grounded via a common resistor.
A voltage for frequency control is supplied to one end of a variable capacitance element for frequency variation via a first low-pass filter, and a modulation signal is supplied to one end of a variable capacitance element for modulation via a second low-pass filter. And a transmission oscillator for outputting a frequency-modulated oscillation signal. 2. The transmission oscillator according to claim 1, wherein a time constant of said second low-pass filter is set sufficiently shorter than a time constant of said first low-pass filter. 3. The transmission oscillator according to claim 1, wherein a variable DC voltage is supplied to one end of said variable capacitance element for modulation. 4. The transmission oscillator according to claim 1, wherein each of said variable capacitance elements is a variable capacitance diode, and an anode of each variable capacitance diode is connected to said resistor. 5. The transmission oscillator according to claim 2, wherein the transmission rate of the modulated signal is 1 Mbps or more. 6. The cut-off frequency of the first low-pass filter is approximately 20 KHz, and the cut-off frequency of the second low-pass filter is approximately 3 MHz for a modulated signal having a transmission rate of 1 Mbps. The oscillator for transmission according to claim 1. 7. A first received intermediate frequency signal is obtained by mixing a received signal with an output signal of a first receiving local oscillator, and this signal is mixed with an output signal of a second receiving local oscillator to obtain a first received intermediate frequency signal. A receiving unit configured to obtain a second receiving intermediate frequency signal; and a transmitting unit configured to generate a transmission signal by mixing the modulated transmission intermediate frequency signal with an output signal of a local oscillator for transmission. The local oscillator and the transmitting local oscillator are shared by one local oscillator, and the transmission intermediate frequency signal and the first reception intermediate frequency signal are set to the same frequency, so that transmission and reception by the signal of the same frequency is time-division-divided. 2. A transmitter / receiver which alternately performs transmission and reception, wherein the transmission oscillator for generating the transmission intermediate frequency signal is the transmission oscillator according to claim 1. 8. A different DC voltage is supplied to one end of the modulation variable capacitance element during transmission and during reception, and an output signal of the transmission oscillator and a first reception intermediate frequency signal are mixed during reception. 8. The transmission local oscillator according to claim 7, wherein the frequency of the mixed output is made to match the frequency of the second reception intermediate frequency signal, whereby the second local oscillator for reception is constituted by the transmission oscillator. Transceiver. 9. A reception signal is mixed with an output signal of a first receiving local oscillator to obtain a first reception intermediate frequency signal, and this signal is mixed with an output signal of a second reception local oscillator to obtain a first reception intermediate frequency signal. A receiving unit configured to obtain a second receiving intermediate frequency signal; and a transmitting unit configured to generate a transmission signal by mixing the modulated transmission intermediate frequency signal with an output signal of a local oscillator for transmission. The local oscillator and the transmitting local oscillator are shared by one local oscillator, and the transmission intermediate frequency signal and the first reception intermediate frequency signal are set to the same frequency, so that transmission and reception by the signal of the same frequency is time-division-divided. A transmission oscillator that generates the transmission intermediate frequency signal includes two variable capacitance elements for frequency variation and modulation, and a low-frequency element having a different time constant at one end of each variable capacitance element. Pass filter , And the other end of each variable capacitance element is DC grounded through a resistor, and a voltage for frequency control is applied to the variable capacitance element for frequency variation through each low-pass filter. A transceiver for supplying a modulated signal to the transmitter.