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CDMA LSI Chip Set - ana - 08-16-2017 CDMA LSI Chip Set [attachment=235] CDMA Portable/Mobile Phone Systems First, consider the signal flow during reception. Figure 1 shows a block diagram of a CDMA portable phone. The very weak receive signal from a base station is down-converted to the IF frequency band by the RF receiver, and amplified by the RX AGC unit. The IF signal is down-converted to an analog baseband signal by the analog baseband processor, and then the analog signal is converted to a digital signal. This digital signal is input to the mobile station modem where it undergoes CDMA demodulation, and is then output to the speaker via the CODEC. CDMA Signal Processing In the receiver, the CDMA spread spectrum modulated IF signal input to the CXA3003R via the RF front-end block is multiplied in the mixer block by an orthogonal local oscillator signal generated inside the CXA3003R. The signals pass through the CDMA low-pass filters and are converted to analog baseband signals, and are then converted into two 4-bit digital signals, I and Q, in the respective A/D converters, before being output. FM Signal Processing In the receiver, the signal path is the same as for CDMA as far as the mixer block. After this, the signals pass through the FM low-pass filters and are converted to FM baseband signals, and are then converted into serial 8-bit digital signals before being output. In the FM transmitter, the FM digital baseband input signal input from the digital processor passes through the D/ A converter and FM low-pass filter, and is converted to an FM analog baseband signal. This signal modulates the transmit VCO frequency (130.38 MHz) and the result is output as an FM modulated signal. Excellent Analog Filter Technology The current service frequency band for CDMA is 800 MHz. Since this frequency band contains powerful waves generated by the AMPS analog FM mobile phone system, very stringent filter characteristic specifications are used to prevent interference from these waves. The provision of an on-chip automatic control filter configuration which determines the gm of the filters in the IC according to the input reference frequency, as shown in figure 3, results in a good frequency characteristic which is unaffected by either temperature fluctuations or element variations . Wide Dynamic Range and Low Noise As a basic principle, CDMA communication requires level adjustment of both receive and transmit signals using AGC. Reception AGC requires a wide input dynamic range, and transmission AGC, a wide output dynamic range. The gain control range in both cases is 80 dB or more, and this must also be achieved with a low noise level. |