Rainbow Electronics AT86RF230 - Manual (Page 46)

46
AT86RF230
5131A-ZIGB-06/14/06
LNA
PA
RFP
RFN
RXTX
0.9V
TX
RX
CM
Feedback
M0
Figure 10-1. Simplified RF Front-end Schematic
A simplified schematic of the RF front end is shown in Figure 10-1. RF port DC values depend on the operating
mode. In TRX_OFF mode, the RF pins are pulled to ground, preventing a floating voltage larger than 1.8V which is
not allowed for the internal circuitry. In receive mode, the RF input provides a low-impedance path to ground when
transistor M0 pulls the inductor center tap to ground. A DC voltage drop of 20 mV across the on-chip inductor can
be measured at the RF pins. In transmit mode, a regulation loop provides a common-mode voltage of 0.9V.
Transistor M0 is off, allowing the PA to set the common-mode voltage. The common-mode capacitance at each pin
to ground is limited to < 30 pF to ensure the stability of this common-mode feedback loop.
10.5. Digital Pins
Pulling resistors are connected to all digital input pins in transceiver state P_ON. Table 10-3 summarizes the pull-
up and pull-down configuration.
In all other states there is no pull-up or pull-down resistor connected to any of the digital input pins.
Pin H = pull-up, L = pull-down
RST
H
SEL
H
SCLK L
MOSI L
SLP_TR L
Table 10-3. Pull-up / pull-down configuration of digital input pins