Figure 4. The gain function can be either an increasing or decreasing

The ideal linear-in-dB scaled transfer function is given by

Equation 1

Equation 1 contains the gain scaling factor of 50 dB/V (20 mV/dB) and the gain intercept of -5 dB, which represents

mV. The deviation from Equation 1, that is, the gain conformance error, is also illustrated in Figure 4. The ripples in

the error are a result of the interpolation action between tap points. The AD8367S provides better than ±0.5 dB of

conformance error over a 40 dB gain range at 70 MHz and better than +1.5/-2 dB at 240MHz over the extended

ambient temperature range of -55C to 110C.

described by

Equation 2

This gain mode is required in AGC applications using the built-in, square-law level detector.

The AD8367S

was designed to operate best in a 200 Ω impedance system. Its gain range, conformance law, and

distortion assume that 200 Ω source and load impedances are used. Interfacing the AD8367S to other common

impedances (from 50 Ω used at radio frequencies to 1 kΩ presented by data converters) can be accomplished using

resistive or reactive passive networks, whose design depends on specific system requirements, such as bandwidth,

return loss, noise figure, and absolute gain range.

The input impedance of the AD8367S

is nominally 200 Ω, determined by the resistive ladder network. This presents a

200 Ω dc resistance to ground, and in cases where an elevated signal potential is used ac coupling is necessary. The

determined by an internal 50 Ω damping resistor, as shown in figure 5. Despite the fact that the output impedance is

50 Ω, the AD8367S should still be presented with a load of 200 Ω. This implies that the load is mismatched, but doing

so preserves the distortion performance of the amplifier.