htrc110 NXP Semiconductors, htrc110 Datasheet - Page 8

• Manufacturer Part Number: htrc110
• Description: Hitag Reader Chip
• Manufacturer: NXP Semiconductors

HTRC110 Hitag Reader Chip
8.2.
The drivers deliver a square shaped voltage to the series resonant antenna circuit. Due to the full
bridge configuration of the drivers this voltage U
sponding to Û
proximately:
8.3.
In order to detect an antenna short or open condition the antenna tap voltage is monitored. An an-
tenna fail condition is reported in the status bit ANTFAIL (see Table 14), if the antenna tap voltage
does not go more negative than the diagnosis level DLEV (see Table 16). This condition is checked
for every coil driver cycle.
8.4.
The crystal oscillator at XTAL1/2 works with either crystal or ceramic resonators. It delivers the
input clock frequency of 4,8,12 or 16 MHz. The oscillator frequency is divided by a programmable
divider to obtain the carrier frequency of 125 kHz (see Table 10). Alternatively, an external clock
signal (CMOS compatible) may be fed into the IC via XTAL1. For example, this signal can be de-
rived from the microcontroller clock.
8.5.
The demodulator senses the absorption modulation applied by a transponder when inserted into the
field. The signal is picked up at the antenna tap point between L
internal resistor R
3). Internally the signal is filtered with a second order low pass filter.
The antenna current and therefore the tap voltage is modulated by the transponder in amplitude
and/or phase. This signal is fed into a synchronous demodulator recovering the baseband signal.
The amplification and the bandpass filter edge frequencies of the demodulator can be adapted to
different transponders via settings in the configuration pages.
The phase between the driver excitation signal and the antenna tap voltage depends on the antenna
tuning. With optimum tuning, the phase of the antenna tap voltage is 90 degrees off the antenna
driver signal. Detuning of the antenna resonant circuit results in a change of this phase relationship.
The HTRC110‘s built-in phase measurement unit allows the measurement of this phase relationship
with a resolution of 360°/64=5.625°. This can be used to compute a sampling time that compensates
the mistuning of the reader antenna. The phase measurement procedure can be carried out:
-
either once before the first communication starts, if the position of the transponder does not
change with the respect to the reader antenna
Antenna Driver, Data Input
Diagnosis
Oscillator / Programmable Divider / Clock
Adaptive Sampling Time Demodulator
drv
=5V. The current flowing through the antenna is sine shaped. It´s amplitude is ap-
dem_in
to a level below 8V (peak) with respect to QGND at the RX-pin (see Figure
Page 8 of 30
Rev. 3.0
drvpp
is approximately 10V (peak-peak) corre-
a
and C
a
. It is divided by R
v
and the
July 2006