MCRF200
DS21219B-page 4
Preliminary
1997 Microchip Technology Inc.
2.0 FUNCTIONAL DESCRIPTION
The RF section generates all the analog functions
needed by the transponder. These include rectification
of the carrier, on-chip regulation of V
PP
(programming
voltage), and V
DD
(operating voltage), as well as high
voltage clamping to prevent excessive voltage from
being applied to the transponder. This section gener-
ates a system clock from the interrogator carrier of the
same frequency, detects carrier interrupts and modu-
lates the tuned LC antenna for transmission to the
interrogator . The chip detects a po wer-up condition and
resets the transponder when sufficient voltage devel-
ops.
2.1 Rectifier – AC Clamp
The AC voltage generated b y the transponder tuned LC
circuit is full wave rectified. This unregulated voltage is
used as the maximum DC supply v oltage f or the rest of
the chip. The peak voltage on the tuned circuit is
clamped by the internal circuitr y to a safe level to pre-
vent damage to the IC. This voltage is adjusted during
programming to allow sufficient programming voltage
to the EEPROM.
2.2 Coil Load Modulation
The MCRF200 communicates by modulating the load
across the tuned LC circuit, which modulates the
received RF field.
2.3 V
DD
Regulator
The device generates a fixed supply voltage from the
unregulated coil voltage.
2.4 V
PP
Regulator
This regulates a programming voltage during the pro-
gramming mode. The voltage is switched into the
EEPROM array to perform block erasure of the mem-
or y as well as single bit programming during both con-
tact and contactless programming. During reading this
voltage is level shifted down and kept below the pro-
gramming voltages to insure that the part is not inad-
vertently programmed.
2.5 Clock Generator
This circuit generates a cloc k with a frequency equal to
the interrogator frequency. This clock is used to derive
all timing in the tag, including the baud rate, modulation
rate, and programming rate.
2.6 IRQ Detector
This circuitry detects an interrupt in the continuous
electromagnetic field of the interrogator. An IRQ (inter-
rupt request) is defined as the absence of the electro-
magnetic field for a specific number of clock cycles.
This feature is used during contactless programming.
2.7 Power On Reset
This circuit generates a power on reset when the tag
first enters the interrogator field. The reset releases
when sufficient power has developed on the V
DD
regu-
lator to allow correct operation. The reset trip points are
set such that sufficient voltage across V
DD
has devel-
oped, which allows for correct clocking of the logic for
reading of the EEPROM and configuration data, and
correct modulation.
2.8 Modulation Logic
This logic acts upon the serial data being read from the
EEPROM and performs two operations on the data.
The logic first encodes the data according to the con-
figuration bits CB6 and CB7. The data can be sent out
direct to the modulation logic or encoded Bi-Phase Dif-
ferential, Bi-Phase Manchester or Manchester with IDI
option.
The encoded data is then either passed NRZ Direct out
to modulate the coil, or FSK modulated, or PSK modu-
lated with changes on the change of data, or PSK with
changes on the bit edge of a one. Configuration bits
CB8 and CB9 determine the modulation option. CB10
is used if the PSK option has been selected, and deter-
mines if the return carrier rate is F
CLK
/2 or F
CLK
/4.