diagram of the amplifier. The main signal path consists of a voltage controlled 0 dB to 45 dB variable attenuator

followed by a 42.5 dB fixed gain amplifier. The AD8367S

is designed to operate optimally in a 200 Ω impedance

system.

Figure 3 Simplified Architecture

The variable attenuator consists of a 200 Ω single-ended resistive ladder that is comprised of nine 5 dB sections and

an interpolator that selects the attenuation factor. Each tap point down the ladder network further attenuates the input

signal by a fixed decibel factor. Gain control is achieved by sensing different tap points with variable transconductance

stages. Based on the gain control voltage, an interpolator selects which stages are active. For example, if only the first

stage is active, the 0 dB tap point is sensed; if the last stage is active, the 45 dB tap point is sensed. Attenuation

weighted average of the discrete tap point attenuations. In this way, a smooth monotonic attenuation function is

synthesized, that is, linear-in-dB with a very precise scaling.

in Figure 4.