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參數(shù)資料
| 型號： | MCP455W |
| 廠商： | Microchip Technology Inc. |
| 英文描述： | 13.56 MHz Read/Write Passive RFID Device |
| 中文描述： | 13.56 MHz讀/寫無源RFID器件 |
| 文件頁數(shù)： | 14/50頁 |
| 文件大小： | 1172K |
| 代理商： | MCP455W |
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MCRF450/451/452/455
DS40232H-page 14
2003 Microchip Technology Inc.
4.0
ANALOG FRONT-END
This section includes high and low voltage regulators,
Power-on Reset, 70 kHz clock generator and
modulation circuits.
4.1
High and Low Voltage Regulator
The high voltage circuit generates the programming
voltage for the memory section. The low voltage circuit
generates DC voltage (V
DD
) to operate the device.
4.2
Power-On Reset (POR)
This circuit generates a Power-on Reset (POR)
voltage. The POR releases when sufficient power has
been developed by the voltage regulator to allow for
correct operation.
4.3
Clock Generator
This circuit generates a clock (CLK). The main clock is
generated by an on-board 70 kHz time base oscillator.
This clock is used for all timing in the device, except for
the Fast mode PPM decoding.
4.4
Data Modulation
The data modulation circuit consists of a modulation
transistor and a LC resonant circuit. The resonant
circuit must be tuned to the carrier frequency of the
Interrogator
(i.e.,
13.56 MHz)
for
maximum
performance.
The modulation transistor is placed between antenna B
and V
SS
pads. It is designed to result in the turn-on
resistance of less than five ohms (R
M
). This small turn-
on resistance shorts the resonant circuit component
between antenna B and V
SS
pads as it turns on. This
results in a change of the resonant frequency of the
resonant circuit. Consequently, the resonant circuit
becomes detuned with respect to the carrier frequency
of the Interrogator. The voltage across the resonant
circuit is minimized during this time. This condition is
called “cloaking”.
The transistor, however, releases the resonant circuit
as it turns off. Therefore, the resonant circuit tunes to
the carrier frequency of the Interrogator again and
develops maximum voltage. This condition is called
“uncloaking”.
The device transmits data by cloaking and uncloaking,
based on the on/off condition of the modulation transis-
tor. Using the 70 kHz Manchester format, the data bit
‘
0
’ will be sent by cloaking and uncloaking the device
for 7
μ
s each. Similarly, the data bit ‘
1
’ will be sent by
uncloaking and cloaking the device for 7
μ
s each. See
Figure 6-1 for the Manchester waveform.
4.5
Detuning Circuit
The purpose of this circuit is to prevent excessive RF
voltage across the resonant circuit.
This circuit monitors V
DD
and detunes the resonant
circuit if the RF coil voltage exceeds the threshold limit
(V
DETUNE
), which is above the operating voltage of the
device.
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