CMX971 Datasheet, PDF (8/25 Pages) CML Microcircuits – Small 16-lead VQFN Package

Quadrature Modulator
CMX971
5 General Description
The CMX971 device is an RF integrated circuit providing a quadrature modulator. A detailed block diagram
for the device is shown in Figure 1. The device can support a wide range of modulation formats and
standards. The following sections describe its functionality.
5.1 Programmable Data Interface
The CMX971 may be controlled via its C-BUS serial interface (see section 6). Alternatively, the device can
be used in direct control mode with reduced programmability; this can be advantageous in systems without
a host controller (see section 7).
5.2 Quadrature Modulator
The quadrature modulator provides translation from baseband I/Q signals to a modulated RF signal. The
wideband inputs can be driven in a differential or single-ended configuration. In the case of single ended
operation a reference voltage equal to the nominal dc level of the modulation must be supplied on the
unused input pin.
5.2.1 DC Offsets and Carrier Leakage
The modulator inputs (TXIN / TXIP and TXQN / TXQP) are differential and require a common dc level or
common mode voltage. Differences in the bias voltages on the pins will result in an increased level of
carrier present at the output. Care should be taken to minimise offsets, thereby minimising carrier leakage.
5.3 Local Oscillator
The LO pin is a single-ended input for the modulator local oscillator signal. Internal ac coupling is provided
so an external dc blocking capacitor is not required, see Figure 4. Note that the LO should be at two or
four times the desired RF output frequency.
 2015 CML Microsystems Plc
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