MLX90121 Просмотр технического описания (PDF) - Melexis Microelectronic Systems

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MLX90121

13.56MHz RFID Transceiver

Melexis Microelectronic Systems  

MLX90121

13.56MHz RFID Transceiver

7. General Description

Power supply

The 90121 requires a nominal 3 or 5 volts external

power supply. Operation is guaranteed between

2.7 and 5.5 Volts. The current drain depends on

the antenna impedance and the output matching

network configuration. Care must be taken about

the power supply: power supply ripple and noise

will severely degrade the overall system

performance.

Transmitter

The output transistor is a low Ron MOSFET. The

drain is directly accessible on the TX pin. A

recommended application schematic optimized to

drive a resistive fifty ohms antenna with a five

volts power supply is provided as a part of this

specification. A simple resonant circuit or/and a

simpler matching network can be connected to the

output. In that case, the general performance and

harmonic suppression will be reduced. 100 %

modulation is achieved by means of gating the

square wave drive of the output transistor. A

variable modulation depth is obtained by means of

switching a resistor in series with the output

transistors’ source connection. An external

resistor provides the default modulation depth

setting. Increasing this external resistor will

increase the modulation depth.

Receiver

The receiver input is typically connected to the

antenna through an external resistor. The

modulation from the tag is then recovered by

means of a diode envelope detector.

FSK and PSK recovery

The demodulated input signal is amplified and

band pass filtered. The signal is then hard limited

by a logarithmic amplifier, and fed to the digital

section. PSK decoded, FSK decoded or a direct

FSK signal can be used for further decoding.

Majority Voting

Both FSK/PSK or ASK can use the Majority

Voting function that will filter for noise and jitter,

that will correct distorted signals and will hence

improve performance.

Reference clock and internal oscillator

The reference clock may be obtained externally

by applying a suitable clock signal to the XTAL1

pin. A sine wave centered at VCC/2 or a CMOS

logic compatible signal is an acceptable external

system clock. The built-in reference oscillator will

work either with a quartz crystal or a ceramic

resonator. The nominal system clock frequency is

13.56 MHz.

Reset defaults and power management

After a power on reset has been performed, the

device is put in its default configuration. There are

three power modes available. In the transmission

mode, the device is fully powered. In the idle

mode, only the reference oscillator is running.

This allows for a fast start up. In the power down

mode, the device internal bias system is

completely switched off, offering essentially a zero

state.

Serial communication interface

The communication interface normally uses 6

wires:

- CK: serial clock input

- DIN: data input

- DOUT: data output

- DSYNC: synchronization output for DOUT

- MODE: configuration or communication

selection input

- RTB: reception or transmission selection

input.

3901090121

Rev. 009

Page 6 of 26

Data Sheet

Sept.-2009

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