Texas Instruments TCM4300 WBD Wbdon, OUT1, Fmrxen Scen, Fmrxen Fmvox, Iqrxen Txen Mode, Synol

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.

WBD	WBD_ON	WBD Demodulator Circuit
Ctrl
			OUT1
MIntCtrl	FMRXEN
	SCEN	SC Clock Generation
			SCEN
	FMRXEN		FMRXEN
	FMVOX	Q-Side Input MUX
DStatCtrl	OUT1	Q-Side RX Enable	VHR High Drive Enable
			(Hi-Z when disabled)
		I-Side RX Enable
	IQRXEN
			IQRXEN
	TXEN		TXEN
	MODE	TX and RX Filter Select
	TXGO
		TX Signal Processing
		PWRCONT, Enable (Hi-z when disabled)

	SYNOL
	PAEN
MStatCtrl	Transmitter
	Control
	Circuits
	TXONIND
	MPAEN

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.

4±19