DESCRIPTION

Demonstration circuit 2391A is optimized for evaluation

of the LTC®5589 low power I/Q modulator up to 4.5GHz.

For frequencies above 4.5GHz, LO matching circuit on

the DC2391A demo board can be easily modified for

improved image rejection performance. Refer to data

sheet for additional information. The four balanced I- and

Q-baseband input ports can be either AC-coupled with

internal bias supplied, or DC-coupled from a source with

a common-mode voltage level of about +1.4V. The SPI

interface is used to set internal registers which control

the gain, optimum center frequency, I-offset, Q-offset and

sideband suppression. In addition to the digital gain control

with 1dB steps, there is an analog gain control, VCTRL. An

on‑chip thermometer can be used to compensate for the

gain vs temperature variations using a digital gain control

change. The update can either be automatically triggered,

or entirely switched off.