CLC5903 Datasheet | National Semiconductor

Overview The CLC5903 Dual Digital Tuner / AGC IC is a two channel digital downconverter (DDC) with integrated automatic gain control (AGC). The CLC5903 is a key ponent in the Enhanced Diversity Receiver Chipset (EDRCS) which includes one CLC5903 Dual Digital Tuner / AGC, two CLC5957 12-bit analog-to-digital converters (ADCs), and two CLC5526 digitally controlled variable gain amplifiers (DVGAs). This system allows direct IF sampling of signals up to 300MHz for enhanced receiver performance and reduced system costs. The CLC5903 is an enhanced replacement for the CLC5902 in the Diversity Receiver Chipset (DRCS). The main improvements relative to the CLC5902 are a 50% increase in maximum sample rate from 52MHz to 78MHz, a 62% reduction in power consumption from 760m W to 290m W, and the added flexibility to independently program filter coefficients in the two channels. A block diagram for a DRCS-based narrowband munications system is shown in Figure 1. The CLC5903 offers high dynamic range digital tuning and filtering based on hard-wired digital signal processing (DSP) technology. Each channel has independent tuning, phase offset, filter coefficients, and gain settings. Channel filtering is performed by a series of three filters. The first is a 4-stage Cascaded Integrator b (CIC) filter with a programmable decimation ratio from 8 to 20 48. Next there a re two symmetric FIR filters, a 21-tap and a 63-tap, both with independent programmable coefficients. The first FIR filter decimates the data by 2, the second FIR decimates by either 2 or 4. Channel filter bandwidth at 52MSPS ranges from ±650k Hz down to ±1.3k Hz. At 78MSPS, the maximum bandwidth increases to ±975k Hz. The CLC5903’s AGC controller monitors the ADC output and controls the ADC input signal level by adjusting the DVGA setting. AGC threshold, deadband+hysteresis, and the loop time constant are user defined. Total dynamic range of greater than 120d B full-scale signal to noise in a 200k Hz bandwidth can be achieved...