Electronic Design

12-V Variable-Gain Amp Delivers High Gain And Bandwidth

A new dc-coupled VGA (variable-gain amplifier) from Analog Devices delivers high gain and bandwidth at an extended industrial temperature range of –55°C to 125°C and a wide power supply range from +/–3 V to +/–12 V. This voltage range is typically used in industrial and instrumentation applications such as industrial process control, industrial video systems, transducer and display drivers, and radar receivers.

The AD8336 VGA provides 100-MHz bandwidth over a gain range of 60 dB, which the company claims is more than twice the bandwidth of competing VGAs that operate at much lower supply voltages. The AD8336 includes a voltage feedback op-amp at its input that allows the gain to be externally adjusted. The nominal preamp gain is 4X (12 dB), but a gain of 20X (26 dB) can be obtained at a reduced bandwidth. The AD8336 operates at a maximum gain range of 0 dB to 60 dB with the preamp gain set to 26 dB.

The AD8336 provides 100-MHz performance over the 60-dB gain range – from –14 dB to +46 dB. A power-adjust pin allows power to be traded for speed in applications that need large supply voltages yet where slower speed is acceptable.

The AD8336 features low power of 150 mW at a +/–3 V supply, low noise of 3.2 nV/ root-Hz, low output offset of less than 50 mV at maximum gain and a slew rate of 450 V/µs for a 2-V step. The inclusion of a voltage feedback op-amp at its input allows the AD8336 to accommodate both inverting and non-inverting topologies, and thereby, a dual polarity VGA. The preamp gain can be set from 12 dB to 26 dB.

The AD8336 is suitable for use with ADCs. In addition, it can be controlled by many types of DACs, including unipolar and bipolar DACS, since the gain control input is differential to the AD8336 and the gain control common-mode voltage increases with increasing supply.

The AD8336 is sampling now and is available in a 4-mm by 4-mm, 16-lead LFCSP (lead-frame chip-scale package). It will be available in volume production in October 2006. The VGA is priced at $4.59 in 1000-piece quantities.

Analog Devices

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