EV9900A Datasheet, PDF (16/27 Pages) CML Microcircuits – Test Access for Important Signals

Evaluation Kit for CMX990
EV9900A
6. Detailed Description
The CMX990 datasheet (not included but available at www.cmlmicro.com) should be referred to
for a detailed description of the CMX990 device.
The EV9900A functionality includes:
• Demonstration of the CMX990 RF functionality at ≈400MHz (or ≈800MHz by component
changes. Please contact CML for further information.)
• Demonstration of EN 300 113 receive performance.
• Interfaces that allow the card to be connected to a host µController, to allow real-time control,
or to a PC (a separate interface may be required)
• An interface allowing the connection of an external reference clock
In summary, the EV9900A allows the user to create experiments to investigate all aspects of the
CMX990 device. The EV9900A is designed to allow user modification, to support detailed
investigation of each user’s specific and different applications.
6.1 Hardware Description
Front End LNA
The PCB includes a 400MHz discrete bipolar LNA using TR5, which is designed for 410-430MHz
and to meet EN 300 113 requirements. The LNA includes some front-end band-pass filtering
(L26, L27, C186, C187, C188, C189, C192, C193 and C194). This can be re-configured for
operation on other bands with value changes. A 1.8dB Pi attenuator (R162, R173, R174) follows
the LNA output.
SAW Image Filter
By fitting or not fitting certain components the user is able to select either a SAW filter (FL1) or
additional T attenuation (R206, R207, R139) to simulate the typical system loss of such a filter. As
built, the SAW filter is not fitted, with the attenuator values fitted to give around 3dB loss.
Mixer Input
The signal from the LNA and filter is then applied to the differential input of the CMX990 RX mixer
via a balun transformer T3. The input is matched for the particular band of interest (L5, L33, L28).
IF Filter
The IF filter (F1A, F1B) is a 45.1MHz 4-pole crystal filter. The pass-band of the filter fitted to the
EV9900A is approximately +/-7.5kHz, designed for 25kHz channel spacing, however other filters
are available in the same package outline, offering different bandwidths (e.g. +/-3.75kHz for
12.5kHz channel spacing). Correct matching of the filter is necessary to achieving optimum
performance.
Reference Oscillator
A 14.4MHz VCTCXO is provided on the PCB (U1). If U1 is disabled (lifting R1), C4 is removed,
and C3 fitted, an alternative clock source can be applied to J1.
© 2007 CML Microsystems Plc
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