Portable radio device

Details Portable radio device Portable radio device

1998-11-17

2001-05-01

Chang, Vivian (Department: 2682)

Telecommunications

Transmitter and receiver at same station

Radiotelephone equipment detail

C455S039000, C455S076000

Reexamination Certificate

active

06226537

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a portable radio device to be used in mobile communication and, more particularly, to make the radio device compact, lightweight, portable in which the amount of electric current to be dissipated is reduced.
A TDMA/FDD (time division multiple access/frequency division duplex) scheme is employed in a personal digital cellular telecommunication system (PDC) to be used for digital mobile communication. In the TDMA/FDD scheme, a transmission frequency is distinguished from a receiving frequency, and an access signal is transmitted to the base station from each mobile station during a set of predetermined time intervals. The portable radio device is provided with high-speed switching performance so as to be able to quickly respond to switching of a radio communication channel of the mobile station while the mobile station is on the move. Further, the portable radio device requires an oscillation circuit capable of ensuring a high degree of frequency stability after switching operations.
In a conventional radio device, a phase-locked loop (PLL) synthesizer is used as an oscillation circuit. In the PLL synthesizer, a frequency divider divides a frequency signal output from a voltage-controlled oscillator (VCO) into a frequency substantially equal to a reference frequency signal. A phase comparator compares the thus-divided frequency signal with the reference frequency signal, thus calculating a phase difference between the signals. The result of such comparison is amplified and converted into a dc voltage by means of a low-pass filter. The dc voltage is delivered to a control terminal of the VCO, thus controlling the frequency signal output from the VCO.
One example of a radio communications device having such a synthesizer is described in Unexamined Japanese Patent Publication 7-283751.
As shown in
FIG. 4
, the radio communications device comprises an antenna
21
; an antenna multiplexer
22
shared between signal receiving and signal transmission; a transmission circuit
23
for converting the frequency of a modulated transmission signal into a transmission frequency; a modulation circuit
24
for modulating a voice signal; a transmission frequency synthesizer
25
for supplying a local signal to the transmission circuit
23
; a receiving circuit
27
which converts a received signal into an intermediate frequency signal by amplification of the received signal; a receiving frequency synthesizer
29
for supplying a local signal to the receiving circuit
27
; a demodulation circuit
28
for extracting a voice signal from the intermediate frequency signal; an intermediate frequency synthesizer
26
for supplying a local signal to the modulation circuit
24
and the demodulation circuit
28
; a reference frequency generation circuit
30
for supplying a reference frequency signal to the individual frequency synthesizers
25
,
26
, and
29
; a power supply
33
composed of batteries; a transmission circuit power on/off switch
31
for turning on or off the power fed to a transmission system circuit; a receiving circuit power on/off switch
32
for turning on or off the power fed to a receiving system circuit; and a CPU
34
for controlling the individual frequency synthesizers
25
,
26
,
29
and the individual power on/off switches
31
and
32
.
The reference frequency generation circuit
30
comprises an original reference frequency generation circuit
30
B consisting of a stable quartz oscillation circuit and a reference frequency signal preparation circuit
30
A which prepares a reference frequency signal by division of the original reference frequency and supplies the thus-prepared reference frequency signal to the individual frequency synthesizers
25
,
26
, and
29
while the phase difference between the reference frequency signal and the original reference frequency signal is maintained.
In this radio communications device, the signal received by the antenna
21
is delivered to the receiving circuit
27
by way of the antenna multiplexer
22
, where the signal is converted into an intermediate frequency signal. The thus-converted intermediate frequency signal is input to the demodulation circuit
28
, where a voice signal and a digital signal are extracted from the intermediate frequency signal.
In contrast, at the time of transmission, the modulation circuit
24
modulates a transmission intermediate frequency through use of the voice signal and the digital signal. In the transmission circuit
23
subsequent to the modulation circuit
24
, the thus-modulated signal is converted into a transmission radio frequency and is transmitted from the antenna
21
by way of the antenna multiplexer
22
.
The original reference frequency signal generation circuit
30
B of the reference frequency signal generation circuit
30
oscillates a stable original reference frequency signal, and the reference frequency signal preparation circuit
30
A generates three reference signals which are 120° out of phase with one another after division of the frequency of the original frequency signal to a certain extent. These three frequency signals are divided and delivered to the respective frequency synthesizers
25
,
26
, and
29
.
To perform the operations set forth, the reference frequency signal preparation circuit
30
A comprises a frequency divider for dividing the original reference frequency and pulse division means having a three-stage ring counter consisting of three JK flip-flops.
In this radio communications device, the reference frequency signals are divided and delivered to the respective frequency synthesizers, thereby preventing an overlap among the operation phases of the frequency synthesizers and concentration of a load current on the individual frequency synthesizers. In this way, there can be prevented a variation in the oscillation frequency of each frequency synthesizer.
Making a portable radio communications device portable and lightweight for convenience of portability and saving of power consumption for long battery life are absolute necessities. For these reasons, various ideas have been conceived.
In the foregoing radio communications device, power is supplied from the power supply
33
to the receiving circuit
27
, the demodulation circuit
28
, and the receiving frequency synthesizer
29
by way of the receiving circuit power on/off switch
32
only during a period of time in which a signal is being received. Further, the radio communications device is configured in such a way that power is supplied from the power supply
33
to the transmission circuit
23
, the modulation circuit
24
, and the transmission frequency synthesizer
25
only during a period of time in which a signal is being transmitted.
To make the radio communications device compact and lightweight, sharing of a variety of constituent elements has already been adopted. For example, the reference frequency signal produced in the reference signal generation circuit
30
of the previously-described radio communications device is utilized not only as a reference signal for the individual synthesizers but also as an operation clock signal of a digital control circuit for controlling the pulse division means.
If the configuration intended to make the portable radio communications device compact and lightweight and to save power consumption deteriorates the characteristics of the radio communications device, a total loss of effectiveness will result. Even in a case where the reference frequency signal generated by the reference signal generation circuit is used also as the reference signal for the frequency synthesizer and as an operation clock signal for the digital control circuit, there arises a phenomenon in which undesired noise components produced by the digital control circuit flow through the operation clock signal line in a reverse direction and are mixed into the reference frequency signal of the frequency synthesizer.
To prevent such a phenomenon, as shown in
FIG. 5
, a buffer amplifier
2
is interposed between a digital control cir

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