On-chip stimulus generation for test and calibration of NFC reader receivers
A method of determining a calibration of a near field communication, NFC, device, the NFC device comprising a receiver circuit, a transmitter circuit and a load modulator circuit, the method comprising: generating a carrier signal in the transmitter circuit, generating a modulation signal in the load modulator circuit, generating a modulated carrier signal, comprising first and second frequencies, by applying the modulation signal to the carrier signal, applying the modulated carrier signal at an input of the receiver circuit, and determining a response parameter of the receiver circuit on the basis of the response of the receiver circuit to the first and second frequencies in the modulated carrier signal.
1. A method of determining a calibration of a near field communication, NFC, device, the NFC device comprising a receiver circuit, a transmitter circuit and a load modulator circuit, the method comprising:
activating a calibration mode in which the load modulator circuit is configured to be operational concurrently to each of the receiver circuit and the transmitter circuit;
generating a carrier signal in the transmitter circuit,
generating a modulation signal in the load modulator circuit by switching a resistance in the load modulator circuit to a resistance that is lower than a resistance in the load modulator circuit when the NFC device is operating in a card emulator mode,
generating a modulated carrier signal, comprising first and second frequencies, by applying the modulation signal to the carrier signal,
applying the modulated carrier signal at an input of the receiver circuit, and
determining a response parameter of the receiver circuit on the basis of the response of the receiver circuit to the first and second frequencies in the modulated carrier signal.
2. A method according to claim 1 , wherein the determined response parameter is the second order input intercept point.
3. A method according to claim 1 , wherein the response parameter is determined on the basis of the response at an intermodulation frequency, f IM2 , corresponding to:
f IM2 =f 1 −f 2 −f IF
where f 1 and f 2 are the first and second frequencies respectively and f IF is an intermediate frequency of an amplifier in the receiver circuit.
4. A method according to claim 3 , wherein f IF =0.
5. A method according to claim 3 , wherein f IM2 is within the bandwidth of the receiver circuit.
6. A method according to claim 1 , further comprising adjusting a parameter of a component within the receiver circuit to thereby alter the response parameter.
7. A method according to claim 6 , wherein repeated determinations of the response parameter are made, each with a different value of the parameter to thereby determine an optimum value of the parameter.
8. A method according to claim 6 , wherein the parameter is a bulk voltage of a transistor in the receiver circuit.
9. A method according to claim 1 , further comprising determining a received noise level at the receiver circuit in the absence of the applied modulated carrier signal.
10. A near field communication, NFC, device, comprising a receiver circuit, a transmitter circuit and a load modulator circuit, wherein the device is configured to:
activate a calibration mode in which the load modulator circuit is configured to be operational concurrently to each of the receiver circuit and the transmitter circuit;
generate a carrier signal in the transmitter circuit,
generate a modulation signal in the load modulator circuit by switching a resistance in the load modulator circuit to a resistance that is lower than a resistance in the load modulator circuit when the NFC device is operating in a card emulator mode,
generate a modulated carrier signal, comprising first and second frequencies, by applying the modulation signal to the carrier signal,
apply the modulated carrier signal at an input of the receiver circuit, and
determine a response parameter of the receiver circuit on the basis of the response of the receiver circuit to the first and second frequencies in the modulated carrier signal.
11. An NFC device according to claim 10 , wherein the device forms a part of at least one of: a mobile telephone, a tablet computer, a laptop computer or a smart phone.
12. A non-transitory computer readable medium comprising a computer program product, which comprises computer readable instructions which, when run on a computer system, cause the computer system to:
activate a calibration mode in which the load modulator circuit is configured to be operational concurrently to each of the receiver circuit and the transmitter circuit;
generate a carrier signal in the transmitter circuit,
generate a modulation signal in the load modulator circuit by switching a resistance in the load modulator circuit to a resistance that is lower than a resistance in the load modulator circuit when the NFC device is operating in a card emulator mode,
generate a modulated carrier signal, comprising first and second frequencies, by applying the modulation signal to the carrier signal,
apply the modulated carrier signal at an input of the receiver circuit, and
determine a response parameter of the receiver circuit on the basis of the response of the receiver circuit to the first and second frequencies in the modulated carrier signal.