Evaluation Kit for CMX838 Family Radio Processor
23
EV8380 User Manual
5.6
How to Utilize the External Signal Processing Paths
The CMX838 supports the use of external signal companding and/or scrambling by way of integrated
circuit-switched paths. For example, if it is desired to scramble the Tx audio signal, the signal can be routed
off-chip by way of the AUDIO OUTPUT SELECT multiplexer (bits 2 and 1 of SETUP register, $80). The
scrambler output can then be fed back into the CMX838 by the use of the AUDIO INPUT 2 SELECT
multiplexer (bits 4 and 3 of SETUP register, $80).
6 Hardware
6.1
Hardware Description
6.1.1 Operating Voltage
There is no on-board voltage regulator on the EV8380. The board was designed in this manner to allow for
ease of testing at a variety of ‘real-world’ operating voltages. As a result, the EV8380 operating voltage (VDD
is set by adjustment of the board’s external power supply.
)
6.1.2 Current Measurement
CMX838 supply current may be directly measured by removing jumpers E7 (computer interface current
measurement), E8 (SVDD measurement), or E10 (VDD measurement) and replacing each removed jumper with
a current meter.
6.1.3 RF Connections
There are three SMB connectors on the EV8380 to allow connections to external RF circuits:
1. “CPOUT”: (SM1 on schematic) Charge pump output current is available at this point. This connection
should be connected to the external loop filter input.
a. Pads are available on the EV8380 board for the addition of user selected loop filter
components and/or an amplifier for the charge pump output signal. Jumpers E14 and E15
allow various charge pump & loop filter configurations.
2. “RF”: (SM2 on schematic) This connector is the injection point for the synthesizer RF negative input (i.e.
VCO output).
3. “REFIN”: (SM3 on schematic) The output of the external RF reference oscillator (i.e. VC/TCXO) should be
connected here.
6.1.4 Clock/Oscillator
Flexible clock generation capabilities allow the CMX838 baseband clocks to be derived from the RF reference
oscillator, a dedicated crystal oscillator circuit, or an externally applied signal of suitable frequency and
amplitude. A 4.0MHz crystal is provided on the EV8380 for baseband clock generation. Two jumpers, E1
and E2, which are normally fitted, enable the on-board crystal oscillator.
For lowest cost, more synchronized, designs use an RF reference oscillator signal for baseband clock
generation instead of an external crystal or external baseband clock signal. To do this:
1) Connect an external RF reference oscillator to the “REFIN” SMB connector on the EV8380 board.
a. Please note that the reference oscillator frequencies compatible with the CMX838 are listed in the
CMX838 data bulletin.
2) Write a data byte to the SYNTHESIZER BASEBAND CLOCK CONTROL ($89) register to configure
the CMX838 clock generation circuits. For example, if the external RF reference oscillator operates at
12.8MHz, a byte of $90 will enable baseband clock generation from the external 12.8MHz reference
oscillator.
7 Circuit Schematics
Three components on the EV8380 are socketed for quick replacement, as necessary, to support customer
testing. R3, a pullup resistor for the microphone, is socketed to allow for different impedance microphones to
be used with the EV8380. R15 is user-selectable to allow for various charge pump current levels.
Jumpers E14 and E15 have solder links installed which direct the charge pump output current directly to the
“CPOUT” SMB connector. These jumpers can be modified to support various user selected charge pump
current schemes.
¤2001 MX-COM, Inc.
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
www.mxcom.com tel: 800 638 5577 336 744 5050 fax: 336 744 5054
Doc. # 20480230.001
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