Texas Instruments TRF7970A Instruction Manual page 26

TRF7970A
SLOS743K – AUGUST 2011 – REVISED APRIL 2014
7
6
5
4
3
2
1
0
0 0.25
Figure 6-5. Digital Internal RSSI (Main and Auxiliary) Value vs RF Input Level in V
This RSSI measurement is done during the communication to the Tag; this means the TX must be on. Bit
1 in the Chip Status Control register (0x00) defines if Internal RSSI or the External RSSI value is stored in
the RSSI Levels and Oscillator Status register (0x0F). Direct command 0x18 is used to trigger an Internal
RSSI measurement.
6.5.1.2 External RSSI
The External RSSI is mainly used for test and diagnostic to sense the amplitude of any 13.56-MHz signal
at the receivers RX_IN1 input. The External RSSI measurement is typically done in active mode when the
receiver is on but transmitter output is off. The level of the RF signal received at the antenna is measured
and stored in the RSSI Levels and Oscillator Status register 0x0F. The relationship between the voltage at
the RX_IN1 input and the 3-bit code is shown in
7
6
5
4
3
2
1
0
0
Figure 6-6. Digital External RSSI Value vs RF Input Level in V
26 Detailed Description
0.5 0.75 1 1.25 1.5 1.75
Input RF Carrier Level in V [V]
25 50 75 100 125
RF Input Voltage Level at RF_IN1 in mV
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2 2.25 2.5 2.75 3 3.25
PP
Figure 6-6.
150 175 200 225 250
PP
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TRF7970A
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3.5 3.75 4 4.25
(V)
PP
275 300 325
(mV)
PP