The ADRF6520 is a matched pair of fully differential low noise and low distortion programmable filters and variable gain amplifiers (VGAs). Each channel is capable of rejecting large, out of band interferers while reliably boosting the wanted signal, thus reducing the bandwidth and resolution requirements on the analog-to-digital converters (ADCs). The excellent matching between channels and their high spurious-free dynamic range over all gain and bandwidth settings make the ADRF6520 ideal for quadrature-based (IQ) communication systems with dense constellations, multiple carriers, and nearby interferers. The filter corners, enable, and dc offset correction loop enable are all programmable via a serial peripheral interface (SPI).
The first VGA that precedes the filters offers 30 dB of continuous gain control with a maximum gain of 18 dB and sets a differential input impedance of 100 Ω. The filters provide a four-pole Butterworth response with −1 dB corner frequencies: 36 MHz, 72 MHz, 144 MHz, 288 MHz, 432 MHz, 576 MHz, and 720 MHz. For operation beyond 720 MHz, the filter can be disabled and completely bypassed, thereby extending the −1 dB bandwidth up to 1.25 GHz. A wideband rms detector is available to monitor the signal at the filter inputs. A fixed gain amplifier of 6 dB immediately follows the filter. The postfilter VGA provides 30 dB of continuous gain control with a maximum gain of 12 dB. The output buffers offer an additional 18 dB of gain and provide a differential output impedance of 20 Ω. The output buffers are capable of driving 1.5 V p-p into 100 Ω loads at better than 55 dBc nominal for the third-order intermodulation distortion (IMD3). Independent, built in, dc offset correction loops for each channel can be disabled via the SPI if fully dc-coupled operation is desired. The high-pass corner frequency is determined by external capacitors on the CHP1 and CHP2 pins and the postfilter VGA gain.
The ADRF6520 operates from a 3.15 V to 3.45 V supply and consumes a maximum supply current of 425 mA. When fully disabled, it consumes ≤10 mA. The ADRF6520 is fabricated in an advanced silicon-germanium BiCMOS process and is available in a 32-lead, exposed pad LFCSP. Performance is specified over the −40°C to +85°C temperature range.
