Low-Distortion PGA Helps ADCs Convert Higher IFs

Cellular basestation designers crave higher intermediate frequencies, which places greater demands on analog-to-digital converters (ADCs). The trend is toward 110, 120, and soon, even 170 Msamples/s. At the same time, 14-bit ADCs require a substantial input-voltage swing.

Aware of this trend, Linear Technology examined existing driver amplifiers and found them wanting. This lack of suitable input amps led the company to develop the LT5514 850-MHz programmable-gain amplifier (PGA). It delivers a 2-V p-p swing into a 200-(omega) load and has second-order and third-order distortion products lower than ­87 dBc.

This improves upon previous amps, most of which could only drive 1 to 1.5 V p-p with third-order distortion products in the mid-60-dBc range. Better PGA performance enhances the spurious-free dynamic range (SFDR) of high-speed ADCs.

Housed in a 20-pin plastic TSSOP, the LT5514 costs $5.20 in lots of 1000.