CMX972 Datasheet, PDF (12/41 Pages) CML Microcircuits – Small 32-lead VQFN Package

Quadrature Demodulator with IF PLL/VCO
CMX972
4.5 Differential Amplifiers
The CMX972 provides two uncommitted differential amplifiers which may be used for a range of purposes.
Two possible configurations are shown in the following sections, however other uses include buffering or
level shifting of the modulator I/Q signals.
4.5.1 I/Q Output Amplifiers
The uncommitted differential amplifiers may be used to convert the differential I/Q output signals to a
single-ended output. A typical configuration of the amplifier on the Q channel (the I channel is identical) is
shown in Figure 7. This circuit has a linear gain of 1.5. Although the circuit is not optimum for rejection of
common mode signals, in practice performance is generally still satisfactory if R4 is omitted (i.e. replaced
with a 0 Ohm link). Users should note that the gain and bandwidth of this stage can be adjusted by altering
the component values and should be configured to suit a particular application.
C1 and C2 may be fitted to provide filtering if required.
RXQN
RXQP
C1
R1
R2
R4
CMX972
OA2P
OA2N
BBAmp2
R3
C2
OA2O
Figure 7 Example External Components – Receive I/Q Output
Note 1:
C1 NF
C2 NF
R1 10kΩ
R2 10kΩ
R3 10kΩ
R4 5kΩ Note 1
The value of R4 should be calculated from the value of the other resistors using the
calculation R4 = R1 – ((R2*R3)/(R2+R3)).
Table 6 Rx I/Q Differential to Single-ended Amplifier Components
 2015 CML Microsystems Plc
12
D/972/2