Telecommunications – Transmitter and receiver at same station – With frequency stabilization
Reexamination Certificate
2000-06-08
2004-03-30
Davis, Temica M. (Department: 2681)
Telecommunications
Transmitter and receiver at same station
With frequency stabilization
C455S552100, C455S082000, C455S083000
Reexamination Certificate
active
06714765
ABSTRACT:
The object of the invention is a transceiver for transmitting and receiving an RF signal on at least two operating frequency ranges.
Mobile communication systems are developing and spreading very fast, and therefore systems of many different standards have been built or are being built in many areas. Therefore there has arisen a need for mobile stations which can be used in more than one system. As examples we can mention the digital systems of the GSM type (Global System for Mobile communications) operating on the frequency ranges 900 MHz, 1800 MHz and 1900 MHz, of which the system with the frequencies 1800 and 1900 MHz are also called DCS and PCN systems. These systems operate on different frequency ranges, but otherwise their specifications are closely related. A problem in realising a transmitter/receiver or transceiver is how to avoid the need for separate transmitter and receiver circuits for all frequency ranges.
From the patent publication EP 653851 there is known a transceiver arrangement which uses one local oscillator having a frequency which is selected between the lower operating frequency range and the higher operating frequency range, so that the same intermediate frequency can be used for the operation on both operating frequency ranges. However, the disadvantage of this solution is that due to the intermediate frequency stages the embodiment is considerably complicate, and the manufacturing costs of the device will be high due to the high number of components.
In a direct conversion receiver, or in a zero intermediate frequency receiver, the radio frequency signal is transformed directly to the baseband without an intermediate frequency. Because no intermediate frequency stages are required the receiver requires only few components, wherefore it is an advantageous solution for many applications, such as mobile stations. Solutions for practical embodiments are described in more detail i.a. in the patent application publication EP 0 594 894 AI.
FIG. 1
shows a previously known block diagram of a mobile station's transceiver, where the receiver is a so called direct transform receiver. There the RF signal received by the antenna is connected with the switch
104
either to the DCS branch or to the GSM branch of the circuit. When receiving a signal of the DCS frequency range the received signal is supplied in the DCS branch to a bandpass filter
106
, an LNA (Low Noise Amplifier)
108
and a bandpass filter
110
. Then from this signal the block
112
generates components with a mutual 90 degrees phase shift. The in-phase component I and the quadrature component Q are further supplied via the switches
114
and
134
to the mixers
116
and
136
.
The mixing signal to the mixers is obtained from the synthesiser
140
having a frequency which corresponds to the received carrier frequency, whereby the obtained mixing results are the in-phase component and the quadrature component of the complex baseband signal. The baseband signal is further supplied to the AGC (Automatic Gain Control)
137
and the correction block
138
for the voltage difference. Then the signal is further processed in the baseband processing unit, block
139
, for the received or the RX signal.
When a GSM signal is received the switch
104
directs the received signal to the GSM branch, which correspondingly has in a series connection a bandpass filter
126
, a low noise amplifier
128
and a bandpass filter
130
. Then the signal is supplied with the same phase to the mixers
116
and
136
. Now the switches
115
and
135
select a signal from the synthesiser as the mixing frequency having a frequency which is divided by two in the block
111
. In block
111
there is formed two signals with a mutual 90 degrees phase shift to the mixers
116
and
136
. Thus the 90 degrees phase shift required by the mixing is not made on the received signal but on the mixing signal. The complex baseband signal from the mixers is supplied to the processing unit
139
for the received baseband or RX signal.
In a known way the synthesiser
140
comprises a PLL (Phase Locked Loop), which comprises a VCO (Voltage Controlled Oscillator)
141
, the output signal of which is amplified by the amplifier
146
in order to generate the output signal. The frequency of the signal provided by the oscillator
141
is divided by an integer Y in the divider
142
, and the resulting signal is supplied to the phase comparator
143
. Correspondingly, the frequency of the signal generated by the reference oscillator
158
is divided by an integer X in the divider
144
and supplied to the phase comparator
143
. The phase comparator outputs a signal which is proportional to the phase difference of said two input signals, whereby the output signal is supplied to an LPF (Low Pass Filter)
145
, and the filtered signal will further control the voltage controlled oscillator
141
. The above described phase locked loop operates in a known way so that the output frequency of the synthesiser is locked to the frequency coming to the phase comparator from the reference frequency branch. The output frequency is controlled by changing the divisor Y.
In the transmitter section the complex baseband transmission signal or TX signal is processed in the TX signal processing unit
160
, from where the complex components of the signal are directed to the mixers
162
and
182
, where the carrier frequency signal is generated by mixing the input signal with the mixing signal. If the DCS frequency is used in the transmission then the switches
111
and
161
select the output signal of the synthesiser
140
as the mixing signal. The obtained DCS signal is supplied to the bandpass filter
168
, the amplifier
170
and the bandpass filter
172
. The generated RF signal is further supplied to the antenna
102
by the switch
180
.
If the transmission is on the GSM frequency range, then the mixing signal is generated by dividing the frequency of the output signal from the synthesiser
140
by two in the divider
161
, from where there is obtained two mixing signals with a mutual 90 degrees phase shift for the first TX mixer
162
and the second TX mixer
182
. The signal at the carrier frequency is supplied by the switches
164
and
184
to the GSM branch, where the in-phase component and the quadrature component obtained from the mixers
162
and
182
are added, block
186
. Then there is filtering and amplification in the blocks
188
,
190
and
192
. The generated RF signal is supplied to the antenna
102
by the switch
180
. Thus at the GSM frequency the 90 degrees phase shift is made on the mixing signal and not on the signal at the carrier frequency obtained as a mixing result.
The above mentioned controllable blocks receive their control from a processing unit (not shown in FIG.
1
), which can contain for instance a microprocessor and/or a DSP (Digital Signal Processor). Further a mobile station comprises a memory unit associated with the processing unit and user interface means, which comprise a display, a keypad, a microphone and speaker, which neither are presented in FIG.
1
.
A problem associated with the solution shown in
FIG. 1
is to obtain a sufficiently accurate phase: the accuracy requirements on the phase difference between the I and Q components is of the order of a few degrees. On the other hand the control of the phase accuracy is complicated by the operation on two frequency ranges far from each other. As the phase shift in conventional RC phase shifters depends i.a. on the frequency and the temperature of the component it is difficult to achieve a sufficiently accurate phase over the whole frequency band and in all operating conditions. In addition the phase accuracy of the synthesiser is lower at the higher frequency range, because the output frequency of the VCO is the same as the RX/TX mixing frequency.
Further, known transceiver arrangements observe only the operation on two frequency ranges. However, as the number of systems operating on different frequency ranges is increasing it is desirable to provide transceiv
Davis Temica M.
Nokia Mobile Phones Ltd.
Perman & Green LLP
LandOfFree
Transceiver for transmitting and receiving an RF signal on... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transceiver for transmitting and receiving an RF signal on..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transceiver for transmitting and receiving an RF signal on... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3216477