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The AD8320 is a digitally controlled variable gain amplifier optimized for coaxial line driving applications. An 8-bit serial word determines the desired output gain over a 36 dB range (256 gain levels). The AD8320 provides linear gain response.
The AD8320 is made up of a digitally controlled variable attenuator of 0 dB to ndash;36 dB, which is preceded by a low noise, fixed gain buffer and followed by a low distortion high power amplifier. The AD8320 has a 220 ohm input impedance and accepts a single-ended input signal with a specified analog input level of up to 0.310 V p-p. The output is specified for driving a 75 ohm load, such as coaxial cable, although the AD8320 is capable of driving other loads. Distortion performance of ndash;57 dBc is achieved with an output level up to 12 dBm (3.1 V p-p) at 42 MHz, while ndash;46 dBc distortion is achieved with an output level up to 18 dBm (6.2 V p-p).
A key performance and cost advantage of the AD8320 results from the ability to maintain a constant 75 ohm output impedance during power-up and power-down conditions. This eliminates the need for external 75 ohm back-termination, resulting in twice the effective output voltage when compared to a standard operational amplifier. Additionally, the on-chip 75 ohm termination results in low glitch output during power-down and power-up transitions, eliminating the need for an external switch.
The AD8320 is packaged in a 20-lead SOIC and operates from a single +5 V through +12 V supply and has an operational temperature range of ndash;40deg;C to +85deg;C.
An evaluation board is available for this product and may be ordered using the following product number: AD8320-EB. Schematic and layout for this evaluation board is contained in the product datasheet.
