Demodulator

• US 20080143435A1
• Filed: 01/25/2006
• Published: 06/19/2008
• Est. Priority Date: 01/25/2005
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Innovision Research & Technology PLC (Broadcom, Inc.)
• Inventors: Wilson, Robin, Miles, David
• Granted Patent: US 8,188,787 B2
• Time in Patent Office: Days
• US Class Current: 329/342
• CPC Class Codes: H03D 1/18 of semiconductor devices

Abstract

A demodulator for demodulating a modulated signal has a peak detector (206) with an input (100) coupled to receive the modulated signal and an output (207) to supply a peak detector output signal. The peak detector has a charge storer (314) coupled to the peak detector output so that the peak detector output signal is provided by a voltage across the charge storer (314) and a comparator (313) having a first comparator input coupled to the peak detector input to receive the modulated signal and a second comparator input coupled to the peak detector output to receive the peak detector output signal. The comparator (313) provides a comparison signal representing a comparison between the voltage of the modulated signal and the peak detector output signal. A charging controller (315, 316 and 318) charges the charge storer (314) so as to increase the output voltage when the comparator (313) provides a first signal indicating that the voltage of the modulated signal is higher than the voltage of the peak detector output signal and discharges the charge storer (314) so as to decrease the output voltage when the comparator (313) provides a second signal indicating that the voltage of the modulated signal is lower than the voltage of the peak detector output signal.

Claims

1. A demodulator for demodulating a modulated signal, the demodulator comprising a peak detector, the peak detector comprising:

a peak detector input coupled to receive the modulated signal and a peak detector output to supply a peak detector output signal;

a charge storer coupled to the peak detector output so that the peak detector output signal is provided by a voltage across the charge store;

a comparator having first and second comparator inputs and a comparator output, the first comparator input being coupled to the peak detector input to receive the modulated signal and the second comparator input being coupled to the peak detector output to receive the peak detector output signal and the comparator being operable to provide a comparison signal representing a comparison between the voltage of the modulated signal and the peak detector output signal; and

a charging controller operable to charge the charge storer so as to increase the output voltage when the comparator provides a first signal indicating that the voltage of the modulated signal is higher than the voltage of the peak detector output signal and to discharge the charge storer so as to decrease the output voltage when the comparator provides a second signal indicating that the voltage of the modulated signal is lower than the voltage of the peak detector output signal.

2. A demodulator according to claim 1, wherein the charging controller comprises a charger operable to charge the charge store, a discharger operable to discharge the charge storer and a coupler controllable by the comparison signal so as to couple the charger to the charge storer to charge the charge storer when the comparer provides the first signal and to disconnect the charger from the charge storer and to enable the discharger to discharge the charge storer so as to decrease the output voltage when the comparer provides the second signal.

3. A demodulator according to claim 2, wherein the coupler comprises a semiconductor switch.

4. A demodulator according to claim 2, wherein the discharger is coupled to the charge storer and is operable to discharge the charge storer more slowly than the charger is operable to charge the charge storer to enable the charger to charge the charge storer when the coupler couples the charger to the charge storer.

5. A demodulator according to claim 2, wherein at least one of the discharger and the charger comprises at least one of a current source and a resistance.

6. A demodulator according to claim 4, wherein the discharger comprises a relatively weak current source and the charger comprises a relatively strong current source.

7. A demodulator according to claim 4, wherein the discharger comprises a resistor and the charger comprises a Field Effect Transistor.

8. A demodulator according to claim 1, wherein the charge storer comprises at least one capacitor.

9. A demodulator according to claim 1, wherein the timing controller comprises a timer operable to supply a control signal when a predetermined time has passed between signals provided by comparator.

10. A demodulator according to claim 9, wherein the demodulator further comprises an OR gate.

11. A demodulator according to claim 1, wherein the demodulator further comprises a sample and hold circuit operable to derive a modulation envelope from the peak detector output signal.

12. A demodulator according to claim 1, further comprising a processor.

13. A demodulator according to claim 12, wherein the processor comprises an analogue to digital converter operable to provide a digital modulation envelope signal.

14. A demodulator according to claim 12, wherein the processor comprises an edge detector.

15. A peak detector for use in a demodulator having the peak detector features set out in claim 1.

16. A near field RF communicator having a demodulator in accordance with claim 1.

17. An NFC communicator having a demodulator in accordance with claim 1.

18. A demodulator for demodulating a modulated signal, the demodulator comprising peak detecting means, the peak detecting means comprising:

a peak detector input for receiving the modulated signal and a peak detector output for supplying a peak detector output signal;

charge storing means coupled to the peak detector output so that the peak detector output signal is provided by a voltage across the charge storing means;

comparator means having first and second inputs and an output, the first comparator input being coupled to the peak detector input to receive the modulated signal and the second comparator input being coupled to the peak detector output to receive the peak detector output signal, the comparator means being for providing a comparison signal representing a comparison between the voltage of the modulated signal and the peak detector output signal; and

a charging control means for charging the charge storing means so as to increase the output voltage when the comparator means provides a first signal indicating that the voltage of the modulated signal is higher than the voltage of the peak detector output signal and for discharging the charge storing means so as to decrease the output voltage when the comparator means provides a second signal indicating that the voltage of the modulated signal is lower than the voltage of the peak detector output signal.