AD8369

The AD8369 is a high performance digitally controlled variable gain amplifier (VGA) for use from low frequencies to a 3 dB frequency of 600 MHz at all gain codes. The AD8369 delivers excellent distortion performance: the two-tone, third-order intermodulation distortion is  69 dBc at 70 MHz for a 1 V p-p composite output into a 1 kW load. The AD8369 has a nominal noise figure of 7 dB when at maximum gain, then increases with decreasing gain. Output IP3 is +19.5 dBm at 70 MHz into a 1 kW load and remains fairly constant over the gain range.

The signal input is applied to pins INHI and INLO. Variable gain is achieved via two methods. The 6 dB gain steps are implemented using a discrete X-AMP® structure, in which the input signal is progressively attenuated by a 200 W R-2R ladder network that also sets the input impedance; the 3 dB steps are implemented at the output of the amplifier. This combination provides very accurate 3 dB gain steps over a span of 45 dB. The output imped- ance is set by on-chip resistors across the differential output pins,