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OM25180FDKM Datasheet(PDF) 74 Page - NXP Semiconductors |
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OM25180FDKM Datasheet(HTML) 74 Page - NXP Semiconductors |
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74 / 149 page  PN5180 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2016. All rights reserved. Product data sheet COMPANY PUBLIC Rev. 3.0 — 7 October 2016 240930 74 of 149 NXP Semiconductors PN5180 High-performance multi-protocol full NFC Forum-compliant frontend 11.8.9.2 Automatic Gain Control The Automatic Gain Control (AGC) of the receiver is used to control the amplitude of the received 13.56 MHz input sine-wave signal from the antenna (input pins RXP and RXN). It is desirable to achieve an input voltage in the range of 1.5 V to 1.65 V at the pins RXP, RXN. For symmetric antennas, the voltage levels are the same on the pins RXP, RXN. A voltage lower than 1.5 V lead to a reduced sensitivity of the receiver, a voltage level higher than 1.65 V could result in clipping of the received signal in the signal processing unit of the PN5180. Both conditions should be avoided for optimum performance of the IC. An antenna detuning caused by the presence of a card, or mobile phone will typically result in an RX input level which is outside the desired input voltage range. Here the AGC helps to simplify the design by keeping the RX voltage automatically within the range of 1.5 V to 1.65 V even under dynamic changing antenna detuning conditions. Functional description: The peak of the input signal at RXP is regulated to be equal to a reference voltage (internally generated from the supply using a resistive divider). Two external resistors are connected to the RX inputs, the specific value of these resistors in a given design depends on the selected antenna and needs to be determined during development. This external resistor, together with an on-chip variable resistor connected to VMID, forms a resistive voltage divider for the signal processor input voltage. The resolution of the variable resistor is 10 bits. By varying the on-chip resistor, the amplitude of the input signal can be modified. The on-chip resistor value is increased or decreased depending on the output of the sampled comparator, until the peak of the input signal matches the reference voltage. The amplitude of the RX input is therefore automatically controlled by the AGC circuit. The internal amplitude controlling resistor in the AGC has a default value of 10 kOhm typ DC coupled. (i.e. when the resistor control bits in AGC_VALUE_REG <9:0> are all 0, the resistance is 10 k). As the control bits are increased, resistors are switched in parallel to the 10k resistor thus lowering the combined resulting resistance value down to 20 Ohm DC coupled (AGC_VALUE_REG <9:0>, all bits set to 1). 11.8.9.3 RX Wait The guard time rx_wait is started after the end of a transmission. If the register flag RX_WAIT_RFON_ENABLE is set to 1 the guard time is started when the device switches off its own RF-Field and an external RF-Field was detected. The guard time rx_wait can be disabled by setting the register RX_WAIT_VALUE to 00h meaning the receiver is immediately enabled. 11.8.9.4 EMD Error handling EMVCo The PN5180 supports EMD handling according to the EMVCo standard. To support further extension the EMD block is configurable to allow adoption for further standard updates. The PN5180 supports automatically restart of the receiver and CLIF timer1 is restarted in case of an EMD event. The CLIF timer is selectable in the EMD_CONTROL register. |
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