CC2420-RTR1 datasheet(54/92 Pages) TI

54 / 92 page

CC2420

SWRS041B

Page 54 of 89

C381

C391

XTAL

XOSC16_Q1

XOSC16_Q2

C381

C391

XTAL

XOSC16_Q1

XOSC16_Q2

Figure 30. Crystal oscillator circuit

Item

CL= 16 pF

C381

27 pF

C391

27 pF

Table 10. Crystal oscillator component values

32 Input / Output Matching

The RF input / output is differential (RF_N

and RF_P). In addition there is supply

switch output pin (TXRX_SWITCH) that

must have an external DC path to RF_N

and RF_P.

In RX mode the TXRX_SWITCH pin is at

ground and will bias the LNA. In TX mode

the TXRX_SWITCH pin is at supply rail

voltage and will properly bias the internal

PA.

The RF output and DC bias can be done

using different topologies. Some are

shown in Figure 4 and Figure 5.

Component values are given in Table 2.

Using a differential antenna, no balun is

required.

If a single ended output is required (for a

single ended connector or a single ended

antenna), a balun should be used for

optimum performance.

The balun adds the signals from the RF_N

and RF_P. This is achieved having two

paths with equal amplitude response, but

180

degrees

phase

difference.

33 Transmitter Test Modes

CC2420 can be set into different transmit

test modes for performance evaluation.

The test mode descriptions in the following

sections requires that the chip is first

reset, the crystal oscillator is enabled

using the SXOSCON command strobe and

that the crystal oscillator has stabilised.

33.1

Unmodulated carrier

unmodulated

carrier

may

transmitted

setting

MDMCTRL1.TX_MODE

to 2 or 3, writing

0x1800 to the DACTST register and issue

a STXON command strobe. The transmitter

is then enabled while the transmitter I/Q

DACs are overridden to static values. An

unmodulated carrier will then be available

on the RF output pins.

A plot of the single carrier output spectrum

from

CC2420 is shown in Figure 31 below.

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