The LT?5554 is a 7-bit digitally controlled programmable
gain (PG) amplifi er with 16dB gain control range. It
consists of a 50Ω input variable attenuator, followed by
a high linearity variable transconductance amplifi er. The
coarse 4dB input attenuator step is implemented via 2-bits
of digital control (PG5, PG6). The fi ne transconductance
amplifi er 0.125dB step within 3.875dB gain control range
is set via 5-bits digital control (PG0 to PG4). The LT5554
gain control inputs (PGx) and the STROBE input can be
directly coupled to TTL or ECL drivers. The seven parallel
gain control inputs time skew can be eliminated by using
the STROBE input positive transition.
The internal output resistor RO = 400Ω limits the maximum
overall gain to 36dB for open outputs. The internal
circuitry of open output collectors enables the LT5554 to
be unconditionally stable over any loading conditions (including
external SAW fi lters) and provides –80dB reverse
isolation at 300MHz.
The LT5554 is internally protected during overdrive and
has an on-chip power supply regulator.
With 0.125dB step resolution and 5ns settling time, the
LT5554 is suitable in applications where continuous gain
control is required.