LM97593

The LM97593 Dual ADC / Digital Tuner / AGC IC is a two channel digital downconverter (DDC) with integrated 12-bit analog-to-digital converters (ADCs) and automatic gain control (AGC). The LM97593 further enhances National's Diversity Receiver Chipset (DRCS) by integrating a wide-bandwidth dual ADC core with the DDC. The complete DRCS includes one LM97593 Dual ADC / Digital Tuner / AGC 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. A block diagram for a DRCS-based narrowband communications system is shown in .

The LM97593 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 Comb (CIC) filter with a programmable decimation ratio from 8 to 2048. Next there are 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 ±650kHz down to ±1.3kHz. At 65MSPS, the maximum bandwidth increases to ±812kHz.

The LM97593'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 123dB full-scale signal to noise in a 200kHz bandwidth can be achieved with the Diversity Receiver Chipset.