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 –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 –57 dBc is achieved with an output level up to 12 dBm (3.1 V p-p) at 42 MHz, while –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 –40°C to +85°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.
