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TRF7960A
SLOS732G – JUNE 2011 – REVISED MARCH 2020
Table 6-5
shows the minimum characteristics recommended for any crystal used with TRF7960A.
As an alternative, an external clock oscillator source can be connected to pin 31 to provide the system
clock, and pin 30 can be left open.
6.9
Transmitter - Analog Section
The 13.56-MHz oscillator generates the RF signal for the PA stage. The power amplifier consists of a
driver with selectable output resistance of 4 Ω or 8 Ω (typical). The transmit power levels are selectable
between 100 mW (half power) or 200 mW (full power) when configured for 5-V automatic operation.
Selection of the transmit power level is set by bit B4 in the Chip Status Control register (0x00). When
configured for 3-V automatic operation, the transmit power level is typically in the range of 33 mW (half
power) or 70 mW (full power).
The ASK modulation depth is controlled by bits B0, B1, and B2 in the Modulator and SYS_CLK Control
register (0x09). The ASK modulation depth range can be adjusted from 7% to 30% or 100% (OOK).
External control of the transmit modulation depth is possible by setting the ISO Control register (0x01) to
direct mode. While operating the TRF7960A in direct mode, the transmit modulation is made possible by
selecting the modulation type ASK or OOK at pin 12. External control of the modulation type is made
possible only if enabled by setting B6 in the Modulator and SYS_CLK Control register (0x09) to 1.
In normal operation mode, the length of the modulation pulse is defined by the protocol selected in the
ISO Control register (0x01). In case of a high-Q antenna, the modulation pulse is typically prolonged, and
the tag detects a longer pulse than intended. For such cases, the modulation pulse length must be
corrected by using the TX Pulse Length register (0x06).
If the register contains all zeros, then the pulse length is governed by the protocol selection. If the register
contains a value other than 0x00, the pulse length is equal to the value of the register multiplied by
73.7 ns. This means the pulse length can be adjusted from 73.7 ns to 18.8 µs in 73.7-ns increments.
6.10 Transmitter - Digital Section
The digital part of the transmitter is a mirror of the receiver. The settings controlled the ISO Control
register (0x01) are applied to the transmitter just like the receiver. In the TRF7960A default mode (ISO
Mode), the TRF7960A automatically adds all the special signals like start of communication, end of
communication, SOF, EOF, parity bits and CRC bytes.
The data is then coded to modulation pulse levels and sent to the RF output stage modulation control unit.
Just like with the receiver, this means that the external system MCU only must load the FIFO with data
and all the microcoding is done automatically, again saving the firmware developer code space and time.
Additionally, all the registers used for transmit parameter control are automatically preset to optimum
values when a new selection is entered into the ISO Control register (0x01).
The FIFO must be reset before starting any transmission with direct command 0x0F.
22
Detailed Description
Table 6-5. Minimum Crystal Recommendations
PARAMETER
Frequency
Mode of operation
Type of resonance
Frequency tolerance
Aging
Operation temperature range
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SPECIFICATION
13.56 MHz
Fundamental
Parallel
±20 ppm
<5 ppm/year
–40°C to 85°C
NOTE
Copyright © 2011–2020, Texas Instruments Incorporated
TRF7960A
www.ti.com
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