CMX017D6 MX-COM, Inc., CMX017D6 Datasheet - Page 7

• Manufacturer Part Number: CMX017D6
• Description: UHF FM/FSK transmitter
• Manufacturer: MX-COM, Inc.

UHF FM/FSK Transmitter
compensate for the signal frequency components within the loop bandwidth, introducing a frequency
dependant distortion of the modulated RF output signal.
To avoid the modulation distortion the carrier frequency is tuned by the external synthesizer chip, with no
modulating signal applied. The synthesizer control is then disabled, by setting the charge-pump output of the
synthesizer to tri-state. The DC coupled base-band signal, applied to the MODIN pin, then modulates the free
running VCO to generate the FM or FSK output signal.
5.1.3
Unlike in the above two cases, where a fixed reference frequency is used in the PLL, the Two-Point
Modulation technique requires modulation inputs to both the PLL reference oscillator and to the RF VCO
circuits.
The modulation signal should be applied to both modulation inputs with suitable AC/DC levels and with the
correct phase to achieve cancellation of the loop’s feedback. This prevents the radio’s PLL circuitry from
counteracting the modulation process and so provides a clean flat modulation response down to DC.
5.2 Powersave and Zero-Power Modes
It is possible to power down each section of the transmitter independently. This feature may be useful when
the CMX017 is configured, with the CMX018, as a radio transceiver. It allows the transmitter to be powered
on and off, thereby saving power, during the sleep and standby periods.
In SLEEP mode (ENLMOD=’0’ and ENLPA=’0’) all sections of the device are powered down and the current
consumption is reduced to less than 10 A. This is the zero-power mode.
In TRANSMIT-STANDBY mode (ENLMOD=’1’ and ENLPA=’0’) only the PA Driver and Power Amplifier
stages are powered down, while the Modulator and Buffered Oscillator remain active. This powersave mode
allows the external frequency synthesizer to stabilize the channel center frequency prior to the RF
transmission.
In TRANSMIT mode (ENLMOD=’1’ and ENLPA=’1’) both the Modulator and the Power Amplifier sections of
the device are fully operational.
Note: The device can be used as a stand alone “UHF Power Amplifier” by forcing (ENLMOD=’0’ and
ENLPA=’1’). The efficiency is maximized by connecting the V
connected to 3.0V.)
5.3 Lower Output Power Applications
For very short range applications the antenna drive can be taken from the modulator output, MODOUT, at
pin 26. The Power Amplifier is powered down by connecting V
allows the supply current to be minimized and the Modulator output to be enabled or disabled using the
ENLPA input at pin 13.
5.4 Example Schematic and Layout
The following schematic (Figure 4) and printed circuit layout (Figure 5 and Figure 6) present a typical
application interface for the CMX017. To aid legibility, the schematic and layout are available electronically
from the MX-COM website http://www.mxcom.com.
Alternative components and component values are shown on the schematic. These should be selected
according to the intended application. The schematic uses the following ICs:
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
1999 MX-COM, Inc.
A flat modulator response is required down to DC, whilst benefiting from the phase noise
improvements due to the PLL (Two-Point Modulation).
www.mxcom.com Tel: [phone] 744 5050 Fax: [phone]
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WB1315X
AD8532-SO8
CC
CC
2 pin to 0V. (The V
3 and V
CC
4 (pins 1 and 12) to 0V. This
CC
CMX017 Advance Information
1 pin must remain
Doc. # 20480193.003