Low Frequency to 3 GHz, Dual VGA with Output Common-Mode and DC Offset Control

The ADRF6521 is a dual, fully differential, low noise and low distortion variable gain amplifier (VGA). The high spurious-free dynamic range over the gain range makes the ADRF6521 ideal for communication systems with dense constellations, multiple carriers, and nearby interferers.

The VGA has a 21 dB attenuation range with a typical voltage gain of 18 dB. The differential input impedance is 100 Ω, while the differential output impedance is 16 Ω. The ±1 dB gain flatness bandwidth is 2.5 GHz. The output buffers are capable of swinging 1.5 V p-p into 100 Ω loads at >55 dBc for second-order and third-order intermodulation distortion (IMD2 and IMD3), and for second and third harmonic distortion (HD2 and HD3) from low frequency to 1 GHz. Variable output dc offset control is accomplished with the OFS1 and OFS2 pins, and the output common-mode can be controlled with the VOCM pin.

The ADRF6521 flexibly operates from a single +5 V supply or from a range of dual supplies and consumes a total supply current of 200 mA. When fully disabled, it consumes 25 mA typical. The ADRF6521 is fabricated in an advanced silicon-germanium BiCMOS process and is available in a 20-lead, exposed pad, 3 mm × 3 mm LFCSP. Performance is specified over the −40°C to +85°C temperature range.

Applications

* Point-to-point and point-to-multipoint radios

* Baseband IQ receivers

* Diversity receivers

* ADC drivers

* Instrumentation

* Medical

* Dual, matched VGAs

* Maximum voltage gain: 18 dB

* Gain control attenuation range: 21 dB typical for TA = 25°C

* ±1 dB gain flatness bandwidth: 2.5 GHz typical

* IMD2 and IMD3 (1.5 V p-p output level)

* −56.8 dBc typical and −75 dBc typical, respectively, at VGN = 1.5 V, 980 MHz and 1000 MHz tones

* HD2 and HD3 (1.5 V p-p output level)

* −75 dBc typical and −73.7 dBc typical, respectively, at VGN = 1.5 V, fundamental at 500 MHz

* −55.9 dBc typical and −57.5 dBc typical, respectively, at VGN = 1.5 V, fundamental at 1 GHz

* Noise figure:

* 10.5 dB typical at maximum gain and at 500 MHz

* 14.8 dB at maximum gain and at 2 GHz

* Noise figure decreases dB for dB with gain backoff