LT5554

The LT^®5554 is a 7-bit digitally controlled programmable gain (PG) amplifi er with 16dB gain control range. It consists of a 50 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 R_O = 400 limits the maximum overall gain to 36dB for open outputs. The internal ircuitry 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.