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In addition to allowing control of power to external functional modules, these power control bits combined
with other control bits are used to control internal TCM4300 functions. This control system is shown in
Figure 4–9.
Transmitter
Control
Circuits
MStatCtrl
DStatCtrl
WBD
Ctrl
WBD_ON
SCEN
FMRXEN
FMVOX
IQRXEN
TXEN
MODE
TXGO
MPAEN
WBD Demodulator Circuit
SC Clock Generation
Q-Side Input MUX
Q-Side RX Enable
I-Side RX Enable
TX and RX Filter Select
TX Signal Processing
PWRCONT, Enable (Hi-z when disabled)
SCEN
FMRXEN
IQRXEN
TXEN
SYNOL
PAEN
TXONIND
MIntCtrl
FMRXEN
VHR High Drive Enabl
e
(Hi-Z when disabled)
OUT1
OUT1
Figure 4–9. Internal and External Power Control Logic
To allow for further system power savings, the TCM4300 receive I and Q channels are enabled separately
because only the Q side is used in analog mode. The FMVOX bit controls the Q-side input multiplexer. When
FMVOX is high, the QP side of the receiver is connected to the FM input terminal, the QN input is connected
to the VHR reference voltage, and the Q side of the receiver is powered up. The MODE bit controls the
Q-side filter characteristics for digital or analog mode. The IQRXEN bit enables both the I and Q receiver
sides. The bit IQRXEN can be set high while still in analog mode (FMVOX high or MODE low) to allow
sufficient power-up settling time for the external receiver I and Q circuits.
Setting the MODE bit low connects RXQP to the FM input and RXQN to VHR.
In the digital mode (MODE bit set high), setting IQRXEN high turns on both sides of the receiver. The TXEN
enables the internal transmit functions. When the TXEN bit is set low, the PWRCONT output goes to a
high-impedance state and the PAEN output is set low. The TXEN signal can be used to power down most
of the external transmit circuits between transmit bursts.