CMX983 Datasheet, PDF (8/93 Pages) CML Microcircuits – Programmable Channel Filter

Analogue Front End (AFE) for Digital Radio
CMX983
3 General Description
The CMX983 is an Analogue Front End (AFE) for a DSP used in Software Defined Radio systems and acts
as a bridge between the analogue and digital sections of advanced digital radio systems. The device also
performs critical DSP-intensive functions with low operating power thereby reducing the overall system power
consumption.
The receive path accepts differential analogue baseband I/Q signals. These are converted to digital,
decimated and passed through programmable FIR channel filters to simplify host DSP processing and data
extraction. The transmit path accepts digital I/Q data streams. These are up-sampled, interpolated and
converted to analogue format, then driven off-chip for external up-conversion and transmission.
Two fractional-N RF synthesisers are provided which are capable of operating with external VCOs of up to
2.1GHz. These have the advantage, over integer-N synthesisers, of allowing a higher PLL reference
frequency, which gives improved noise performance and agility. The fractional modulator can be configured
for either 16-bit or 24-bit operation, enabling very fine frequency resolution. The synthesisers also include a
fast-lock feature that helps minimise lock time when switching channels and provides an indication of when
lock is achieved.
An auxiliary ADC (with multiplexed inputs) and a number of auxiliary DACs are included for control and
measurement functions such as AFC, AGC and RSSI. The ADC has a digital threshold compare function, and
one of the DACs has a programmable auto-ramping feature that is especially useful for controlling the ramp-
up and ramp-down profile of the transmitter power amplifier.
Five analogue comparators with programmable thresholds are provided; these share the auxiliary ADC input
pins and give the user the option of sensing monitoring signals with very low power consumption.
The CMX983 is clocked from a full-swing logic level, or by low-amplitude sine wave or clipped sine wave. This
may be used directly as a reference source or fed to an on-chip PLL capable of generating a wide range of
internal clock frequencies.
The CMX983 is suitable for radio systems employing channel bandwidths up to 25kHz and is usable in
satellite communication, high performance wireless data and professional two-way radio systems. The
CMX983 features a high level of configurability, supporting numerous sample rates and filtering
characteristics. This configurability enables a high level of functionality, integration and connectivity with RF
building block ICs. The CMX983 connects seamlessly with CML’s CMX994 Direct Conversion Receiver and
the CMX998 Cartesian Feedback Loop Transmitter, to provide a complete, small form factor, RF-to-digitised
baseband solution operating at up to 1GHz.
The Rx and Tx channels interface to the external DSP through dedicated fast serial ports. A separate C-BUS
port is provided for general control and configuration of the CMX983, and a configurable interrupt generator
may be used to minimise the load on the host processor.
 2015 CML Microsystems Plc
8
D/983/6