Evaluation Kit User Manual for CMX017

EV0171

© 1999 Consumer Microcircuits Limited

13

UM0171/2

1.6.1.4 FM/FSK Modulator

The modulation input, MODIN, TP1, is designed to be directly driven by a dc-coupled baseband input

signal, to generate a frequency modulated (FM or FSK) RF signal.

Please refer to the CMX017 device datasheet for specifications on maximum modulation

frequency/voltage at the device input (MODIN, pin 18).

The resistors R6 and R5 can be modified depending on the modulation source and required frequency

deviation.

The output impedance at the CMX017 MODOUT pin is typically 50

Ω. Using microstrip techniques the

MODOUT track on the 4-layer PCB has been designed to provide a line impedance of 50

Ω.

The CMX017 Modulator output signal can be routed to an SMA connector (not fitted), J3, by modifying

components C14, C15, C31 and L7.

1.6.1.5 Power Amplifier

The input/output impedances at the CMX017 PAIN/PAOUT pins are typically 50

Ω. Using microstrip

techniques their tracks on the 4-layer PCB have been designed to provide line impedances of 50

Ω.

Additional power gain improvement is achieved by employing the simple output matching network, C2,

C3 and L2.

Both amplifier output stages, IPAOUT and PAOUT, must have a dc connection to the supply rail

through RF chokes, L4 and L5.

The evaluation device can be used as a standalone UHF Power Amplifier by modifying components

C14, C15, C31 and L7. The RF signal should be input via an SMA connector (not fitted), J3.

1.6.2

Adjustments and Controls

1.6.2.1 Frequency Control

The trimmer potentiometer, RV2, controls the RF operating frequency. The control voltage derived (0-

3V) from this potentiometer allows the RF operating frequency to be set between 860 - 935MHz. The

frequency control potentiometer draws a typical current of 150µA from the AV

1.6.2.2 Gain Control

The trimmer potentiometer, RV1, controls the gain of the CMX017 PA driver. The output power, at the

MODOUT pin, is variable over a 20dB range. The output power is maximum when the CMX017 GAIN

pin is connected to 3V and is reduced by typically 20dB when this pin is connected to 0V.

The gain potentiometer draws a typical current of 150

µA from the AV