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.
