Receiver integrated circuit for mobile telephone

Details Receiver integrated circuit for mobile telephone Receiver integrated circuit for mobile telephone

1997-03-13

2001-05-22

Tsang, Fan (Department: 2746)

Telecommunications

Receiver or analog modulated signal frequency converter

With particular receiver circuit

C455S232100, C375S329000, C375S330000

Reexamination Certificate

active

06236848

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a receiver integrated circuit (hereinafter refereed to as a receiver IC) for use with a mobile telephone and, more particularly, to a receiver IC for a mobile telephone operating in a dual mode environment involving CDMA (code division multiple access) mode and FM (frequency modulation) mode.
FIG. 4
is a block diagram of a common mobile telephone operating in a dual mode environment involving CDMA mode and FM mode. The transmitter (TX) portion of the telephone works and is constituted as follows: signals I and Q output by a modem
101
are QPSK-modulated by a quadri-phase shift keying (QPSK) modulator
102
. The modulated signals are amplified by a transmitter-side variable gain amplifier (TX-AMP; simply called a variable amplifier hereunder)
103
. The amplified signals are mixed by a mixer (MIX)
104
together with a locally oscillated signal from a local oscillator (OSC)
121
, whereby a radio frequency (RF) transmitted signal is produced. The RF transmitted signal is transmitted via a band-pass filter
105
, a power amplifier (PA)
106
, a duplexer
107
and an antenna
108
.
The receiver (RX) portion of the mobile telephone works and is constituted as follows: an RF signal received via the antenna
108
is sent to a mixer (MIX)
111
by way of the duplexer
107
, a low-noise amplifier (LNA)
109
and a band-pass filter
110
. The received signal is mixed by the mixer
111
together with the locally oscillated signal from the local oscillator (OSC)
121
, whereby an IF received signal is produced. The IF received signal is applied both to a CDMA band-pass filter
112
and to an FM band-pass filter
113
. One of output signals from the two filters is selected in accordance with a currently established mode. The selected output signal from the filter is amplified by a receiver-side variable amplifier (RX-AMP)
114
. The amplified signal is demodulated by a QPSK demodulator
115
, and the demodulated signal is sent to the modem
101
.
In the modem
101
, a received signal intensity indication circuit
116
detects the intensity of the received signal. The detected reception intensity is compared with intensity reference data by a comparator
117
. The difference between the detected intensity and the reference data is sent both to a receiver-side AGC voltage correction circuit
118
and to a transmission output correction circuit
119
. The receiver-side AGC voltage correction circuit outputs an AGC voltage such that the difference sent from the comparator
117
will become zero, i.e., that the output of the circuit
116
will coincide with the reference intensity data, whereby the gain of the receiver-side variable amplifier (RX-AMP)
114
is controlled.
The transmission output correction circuit
119
on the transmitter side is supplied both with the difference from the comparator
117
and with transmission output correction data reflecting the line status between the mobile telephone and a base station. A transmitter-side AGC voltage correction circuit
120
outputs an AGC voltage according to the transmission output correction data to control the gain of the variable amplifier (TX-AMP)
103
so that the modulated signal will be inversely proportional to the level of the received signal.
When the mobile telephone of the above constitution is in CDMA mode, signals of −105 dBm through −25 dBm are input to the antenna
108
. This means that the receiver portion must have a dynamic range of at least 80 dB for the received signals. In FM mode, signals of −120 dBm through −20 dBm enter the antenna
108
. In the latter case, the receiver portion must have a dynamic range of at least 100 dB.
Such extensive dynamic ranges are implemented by the receiver-side variable amplifier
114
having a plurality of variable amplifiers cascaded as shown in
FIG. 5
, so that an IF received signal with pronounced level fluctuations will have a constant level at an input terminal of the QPSK demodulator
115
. Harmonic components of the output signal from the variable amplifier
114
are attenuated by the low-pass filter (LPF)
4
, and the resulting signal is input to the QPSK demodulator
115
. By resorting to a 90-degree phase shifter
8
, a PLL divider (
1
/N)
9
and an oscillator
10
, the QPSK demodulator
115
demodulates the input signal back to the initial base-band signals I and Q.
In CDMA mode, signals of −105 dBm to −25 dBm entering the antenna are amplified by the variable amplifier
114
so that they will have a constant level at the input terminal of the QPSK demodulator
115
. In FM mode, of the signals of −120 dBm to −20 dBm entering the antenna, those of −120 dBm to −40 dBm (i.e., for 80 dB) are amplified by the variable amplifier
114
. The remaining signals of −40 dBm to −20 dBm, exceeding the control range of the variable amplifier
114
, are saturated therein and forwarded at a constant level to the QPSK demodulator
115
through limiter operation.
The signals saturated in the variable amplifier
114
generate harmonic components twice to four times those of their unsaturated counterparts. These harmonic components are attenuated by the LPF
4
to 20 dB or less with respect to a fundamental wave. The characteristic of the LPF
4
is illustrated in FIG.
2
. The output signal of the LPF
4
has a CN ratio greater than 20 dB. The QPSK demodulator
115
and an FM digital demodulator installed immediately downstream need to provide a CN ratio greater than 20 dB where the SN ratio of the demodulated signal is desired to be greater than 45 dB. The frequency of the oscillator shown in
FIG. 5
is set to a frequency input to the variable amplifier
114
.
In the conventional setup outlined above, harmonics, especially those of degree two, are characterized for their frequency being close to the signal and having high voltages. This requires that the LPF
4
for attenuating harmonics provide a steep cut-off characteristic depicted in FIG.
2
. The LPF
4
is thus composed generally of an LC circuit and is not conducive to being implemented in IC form. A resonance coil L, included in the oscillator
10
for QPSK demodulation, is too bulky to be formed in IC. Because the resonance coil L needs adjustment after assembly, it cannot be incorporated in an IC arrangement.
One proposed solution to the above difficulties is a setup in which the LPF
4
(with connecting points
6
and
7
) and resonance coil L in
FIG. 5
are both separated and externally furnished while the variable amplifier
114
, QPSK demodulator
115
, 90-degree phase shifter
8
, PLL divider
9
and oscillator
10
are built altogether into IC. One problem with this constitution is that the connecting points
6
and
7
of the LPF
4
are poorly isolated from the input terminal of the variable amplifier
114
. The inadequate isolation makes it difficult to achieve gain control characteristics of 80 dB or more and tends to deteriorate gain slope linearity.
Experiments have shown that between 100 and 300 MHz, the isolation between terminals is about 40 to 50 dB. If the amplifier gain is set to −50 to+40 dB to satisfy other requirements, the necessary attenuation of −50 dB cannot be accomplished. In addition, where lead terminals for connecting the LPF
4
are installed in the IC, an oscillated signal from the resonance coil L reaches the connecting points
6
and
7
of the LPF
4
and the input terminal of the amplifier
114
. The oscillated signal and a signal derived from limiter operation produces beat in the QPSK demodulator
115
, whereby the CN ratio of the signals I and Q is deteriorated.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to overcome the above and other disadvantages of the prior art and to provide a receiver IC for a mobile telephone, the IC comprising a receiver circuit required to provide high-gain characteristics when used in a mobile telephone and the like operating in a dual mode environment involving CDMA mode and FM

Affiliated with

Also associated with

Rating

Receiver integrated circuit for mobile telephone does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Receiver integrated circuit for mobile telephone, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Receiver integrated circuit for mobile telephone will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2552436