Texas Instruments 3138 155 232931 Input / Output Matching, Transmitter Test Modes, CL= 16 pF

XOSC16_Q1

XTAL

C391

CC2420

XOSC16_Q2

C381

Figure 30. Crystal oscillator circuit

Item

C381

C391

CL= 16 pF

27pF

27pF

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.

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

An unmodulated carrier may be

transmitted by setting MDMCTRL1.TX_MODE to 2 or 3, writing

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.

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.

SWRS041B Page 54 of 89