EV9900 Datasheet, PDF (19/27 Pages) CML Microcircuits – Evaluation Kit

Evaluation Kit for CMX990
EV9900
6.2.2 Tx/Rx Switch
The following modifications need to be implemented on the EV9900 (PCB546D) evaluation board
for the RX/TX switch to work at 800/900MHz:
• D1 = BAR63_02W.
• Use a 0R to link out D3’s usual placement. Then D3 should be placed as shown in Figure 4
then is done by removing some PCB solder resist from the long track in the RX path near
J16 (placed in line with leg of J16 as shown below) and also some resist from the nearby
GND plane has to be removed. D3 = BAR63_02W. D3 connections are cathode to GND and
anode to track (signal).
Scratch off resist
from GND and track.
Place cathode end
GND side, indicated
by marking on
device.
Diode placed in line with
leg of TXOUT SMA
Figure 4 – Picture of relevant area for new placement of D3
• C214, C212 and C94 = 1nF
• R194 =150nH (0603CS)
• R202 = 2k2
• C172 = 470pF
• R178 and R201 = NF
The main consequence with this topology is that only one control line is required and the logic is
as follows; TX_ON = 3V (HIGH) => TX mode, TX_ON = 0V (LOW) => RX mode.
6.2.3 External Local Oscillator
To evaluate the performance of the CMX990 it is recommended that a low noise external
oscillator be used for the main LO. This is particularly important when performing blocking and
adjacent channel tests. An external main LO can be supplied via J10. The following changes are
recommended:
• Remove R78, R164 and R200.
• Ensure C98 (1nF) and R149 (18Ω) are fitted.
6.2.4 Intermediate Signal Connections
The EV9900 allows a user to connect signals at various points in the signal path of the IC.
Details can be found on the schematic and in the list of connectors. Users can choose
appropriate matching and configurations to suit their requirements. Note that just connecting test
© 2005 CML Microsystems Plc
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UM9900/1