Digitally programmable IF VGA
23 December 2008
Linear Technology has introduced the LT5554; a broadband digitally programmable gain IF amplifier.
Its gain is digitally controlled from 2dB to 18dB by a 7bit parallel word, producing what the manufacturer claims are the finest 0.125dB steps gain control granularity of any amplifier available. The amplifier settles in less than 5ns from a gain change, producing low glitch noise and supporting fast and accurate AGC (Automatic Gain Control) performance. Its output stage has robust capability to drive into 50Ω loads with low distortion and noise; so it enables high spurious-free dynamic range performance in ADC systems. These characteristics make the LT5554 suitable to drive high-speed, high resolution A/D converters, where the input sampling noise can couple back to the RF and IF circuits.
With the new generation of wireless technology such as LTE (Long-Term Evolution) and WiMAX, which use modulated signals with 12dB crest-factor, the need to maintain linearity performance over wide operating levels is important for producing consistent basestation performance. Additionally the LT5554 has excellent gain accuracy of ±0.1dB from -40°C to +85°C. The new model is powered from a single 5V supply. It draws a nominal supply current of 200mA. The chip can be shutdown via an ENABLE pin. When in shutdown the device draws a typical supply current of 4mA, and a maximum of 5.1mA. The device comes in a 32-lead, 5mm x 5mm plastic QFN surface mount package.
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