CMX971 Datasheet, PDF (7/25 Pages) CML Microcircuits – Small 16-lead VQFN Package

Quadrature Modulator
4.2 Quadrature Modulator
A typical circuit for the quadrature modulator output is shown in Figure 3 / Table 4.
CMX971
I Inputs
LO
Q Inputs
CMX971
90°
+
RFOUT
C1
I/Q Modulator
Output
Figure 3 Modulator Output External Components (30MHz to 1GHz)
C1
1nF
Table 4 Quadrature Modulator Output Components
4.3 Local Oscillator (LO) Input
The CMX971 has a single ended LO input. Users should be aware that the presence of high levels of
harmonics in the signal applied to the LO Input might degrade quadrature accuracy.
LO Input
CMX971
Buffer and
Divider
LOGND
Figure 4 LO Input Configuration
A separate ground pin (LOGND) is used for the LO buffer to allow routing of the ground feed to the device
such that any coupling, via the ground plane, between the LO signal and the RF signal can be minimised.
In most cases it will be sufficient to just connect this to the RFGND ground plane, although it may be
advantageous to supply LOGND from the ground supply for the LO generator or to star-connect the LO
generator ground and the LOGND at a single point on the ground plane.
 2015 CML Microsystems Plc
7
D/971/4