LGC-340/345W
21
LGIC
LG Information & Communications, Ltd.
1.2.3 Receive End Bandpass Filter
Receive RF signals (869.04-893.97 MHz) from the LNA are fed into RF BPF. RX RF filter has IL of 3dB
(Max) on the average whereas the ripple of passband is about 2.0dB (Max) and the RF signal suppression rate on
transmit band is 30dB.
The impedance of input/output terminal is 50
Ω
and the maximum power that can be inputted is about 25dBm. IF
BPF for CDMA signals (85.38MHz
¡ ¾
630kHz) can receive the IF signal of 20dBm which is the maximum input
signal from the Down mixer. The side band signal suppression rate is 41dB and IL is 10.3dB.
IF BPF for FM has the 3dB bandwidth of 85.38MHz
¡ ¾
15kHz. IL is 5dB (Max) whereas the ripple of passband is
1.5dB (Max).
1.2.4 Description of IFR3000 Internal Circuit
The IFR3000 is a key circuit element in the Rx signal path of the CDMA/AMPS subscriber unit. It is located
between RF system and the MSM digital processor. The analog inputs of IFR3000 interface directly with the IF
receive circuitry of the subscriber unit. The digital inputs and outputs of IFR3000 interface directly with
MSM3000.
1.2.4.1 CDMA Rx Signal Path
The IFR3000 consists of a received signal path, clock synthesis, buffering circuits and mode control logic.
The CDMA Rx signal path comprises the Rx AGC amplifier, mixer, CDMA low-pass filters, and A/D converters.
With its CDMA_IF and CDMA_IF/ terminals, the IFR3000 receives two IF signals that have been modulated
(CDMA Spreading Power Density Modulation) extending
±
630kHz from 85.38MHz Center Frequency.
The Rx AGC amplifiers or attenuates the received CDMA IF signal to provide a constant-amplitude signal to the
I/Q downconverter.
This type of gain control is the power adjustment function to reduce the loss resulting from the receive power of a
mobile station by maintaining the constant signal strength at the IFR3000 receive end even if the received signals
change according to the location of a mobile station user.
The AGC gain is controlled by varying the DC voltage on the Vcontrol input pin.
The AGC’s 90dB dynamic range is available over the full power supply range of the device. The IF output of the
Rx AGC amplifier is further classified into I and Q signals and downconverted by mixing with quadrature local
oscillator signals. The local oscillator signals are generated by a voltage controlled oscillator onboard the
IFR3000 and frequency stabilized by external varactor-tuned resonant tank circuitry. The I and Q phasing of the
receive section is spectrally inverted from a standard quadrature demodulator when the IF input signal frequency
is above the IF center frequency. The I/Q down converter outputs the CDMA I and Q signals haing the
bandwidth of 1kHz ~630kHz through CDMA LPF. The use of LPF in IFR3000 suppresses spurious signals
entering the receiver in order to improve the CDMA baseband signal selectivity.
