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.