Description
PRODUCT DESCRIPTION
The AD**0 and AD**2 dual channel, low noise variable gain
amplifiers are optimized for use in ultrasound imaging systems,
but are applicable to any application requiring very precise
gain,
low noise and distortion, and wide bandwidth. Each independent
channel provides a gain of 0 dB to **0 dB in the AD**0
and –*0 dB to **0 dB in the AD**2. The lower gain of the
AD**2 results in an improved signal-to-noise ratio at the
output.
However, both products have the same 1.4 nV/ÖHz input
noise spectral density. The decibel gain is directly
proportional
to the control voltage, is accurately calibrated, and is
supplyand
temperature-stable.
To achieve the difficult performance objectives, a proprietary
circuit form—the X-AMP®—has been developed. Each channel
of the X-AMP comprises a variable attenuator of 0 dB to
–*2.*4 dB followed by a high speed fixed gain amplifier. In
this
way, the amplifier never has to cope with large inputs, and can
benefit from the use of negative feedback to precisely define
the
gain and dynamics. The attenuator is realized as a seven-stage
R*2R ladder network having an input resistance of **0 W,
lasertrimmed
to ±2%. The attenuation between tap points is 6.*2 dB;
the gain-control circuit provides continuous interpolation
between
these taps. The resulting control function is linear in dB
