Evaluation Kit for CMX838 Family Radio Processor

23

EV8380 User Manual

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¤2001 MX-COM, Inc.

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Doc. # 20480230.001

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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

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

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.