EV0181 Datasheet, PDF (15/18 Pages) CML Microcircuits – User Manual

Evaluation Kit User Manual for CMX018
EV0181
The CMX018 detector output pin (DETOUT pin 18) can be monitored via TP6. This output is first
amplified using an operational amplifier U3. The amplified output can be monitored at AUDOUT,
TP10. The level measured at AUDOUT will be typically 0.5Vrms for a 1kHz RF modulated input with a
modulation level of 100kHz.
The second amplifier (B) in the U1 package is also configured as a comparator to provide a digital
output of the signal at AUDOUT. The threshold level is set to half supply using the potential divider
resistors R7and R8.
Note, the audio amplifier and data output stage is not a ‘total’ solution. It is designed to show that data
can be recovered and should give reasonable BER for RF input levels >-90dBm (high gain mode).
This output circuitry may need to be modified or bypassed depending on the user’s application.
Reception of large continuous streams of 1’s or 0’s will not be possible unless the ac coupling
capacitors, C53 and C54, are bypassed.
1.6.2 Adjustments and Controls
1.6.2.1 Frequency Control
The trimmer potentiometer, RV1, controls the local oscillator frequency. The control voltage derived
(0-3V) from this potentiometer allows the RF operating frequency to be set between 860 - 935 MHz
(90MHz below local oscillator).
Using a DVM, monitor the dc voltage at RSSI. Set the RF operating frequency (860 - 935 MHz) by
slowly adjusting the frequency potentiometer, RV1. Adjust RV1 until the dc level at RSSI is maximum.
RV1 may need to be adjusted several times due to drift and settling time of the potentiometer.
The frequency control potentiometer draws a typical current of 150µA from the AV_DD2 supply.
1.6.2.2 10.7MHz Quadrature Tank Tuning
The trimmer capacitor, CV1, allows the user to tune the 10.7MHz quadrature tank circuit.
1.6.2.3 Enable and Gain Select
The evaluation device enable and gain select lines are controlled by switch SW1.
Switch SW1:1 allows the user to configure the CMX018 for zero-power. With SW1:1 in the ‘on’
position the device is enabled (default), and when SW1:1 is in the ‘off’ position the device is in zero-
power mode.
The LNA switched gain function which is used to increase the dynamic range of the receiver, is
controlled by gain select switch SW1:2. In the ‘off’ position the LNA will be in high gain mode, and low
gain selected when in the ‘on’ position (default).
© 1999 Consumer Microcircuits Limited
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