Texas Instruments 3138 155 232931 manual CC2420

					CC2420
		RBW	10 kHz	RF Att	30 dB
Ref Lvl		VBW	10 kHz
3 dBm		SWT	50 ms	Unit	dBm
3
0					A
-10
-20
-30 1AVG					1SA
-40
-50
-60
-70
-80
-90
-97
Center 2.45 GHz		200 kHz/		Span 2 MHz
Date:	23.OCT.2003	21:38:33

Figure 31. Single carrier output

33.2 Modulated spectrum

The CC2420 has a built-in test pattern generator that can generate pseudo random sequence using the CRC generator. This is enabled by setting MDMCTRL1.TX_MODE to 3 and issues an STXON command strobe. The modulated spectrum is then available on the RF pins. The low byte of the CRC word is transmitted and the CRC is updated with 0xFF for each new byte. The length of the transmitted data sequence is 65535 bits. The transmitted data-sequence is then:

[Synchronisation header] [0x00, 0x78, 0xb8, 0x4b, 0x99, 0xc3, 0xe9, …]

Since a synchronisation header (preamble and SFD) is transmitted in all TX modes, this test mode may also be used to transmit a known pseudorandom bit

sequence for bit error testing. Please note

that CC2420 requires symbol

synchronisation, not only bit synchronisation, for correct reception. Packet error rate is therefore a better measurement for the true RF performance.

Another option to generate a modulated spectrum is to fill the TXFIFO with pseudo-

random data and set MDMCTRL1.TX_MODE to 2. CC2420 will then transmit data from the FIFO disregarding a TXFIFO underflow. The length of the transmitted data sequence is then 1024 bits (128 bytes).

A plot of the modulated spectrum from CC2420 is shown in Figure 32. Note that to find the output power from the modulated spectrum, the RBW must be set to 3 MHz or higher.

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