ANALOGUE-TO-DIGITAL CONVERTER

• US 20100151900A1
• Filed: 05/18/2007
• Published: 06/17/2010
• Est. Priority Date: 05/18/2007
• Status: Active Grant

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Koli, Kimmo
• Granted Patent: US 8,274,418 B2
• Time in Patent Office: Days
• US Class Current: 455/550.100
• CPC Class Codes: G11C 27/024 using a capacitive memory element G11C27/04 takes precedence
• CPC Class Codes: H03M 1/1215 using time-division multiplexing
• CPC Class Codes: H03M 1/468 in which the input S/H circuit is merged with the feedback DAC array

Abstract

An analogue to digital converter uses charge sampling in combination with a successive approximation conversion technique in order to combine anti-alias filtering and quadrature downconversion functions into the data converter. The conversion method is an energy-efficient realization for wide-band radio systems with moderate resolution specifications such as 4G or ultra-wideband radio (UWB). The converter uses two capacitor matrices, one to perform charge sampling, and one to be used simultaneously in the successive approximation technique, so that full use of an input signal is made and efficiency is maximised.

Claims

1. A method of converting an analogue signal to a digital signal, comprising:

converting an input analogue voltage signal to a current signal;

applying the current signal to a charge-storage means during a sampling period;

performing approximation of a voltage derived from charge stored during the sampling period by determining one of a successively smaller range of voltages which corresponds to the derived voltage; and

outputting a digital signal corresponding to the approximated voltage.

2. A method according to claim 1 comprising alternately applying the current signal to a first charge-storage means and a second charge-storage means, wherein the approximation of a voltage derived from charge stored in the first charge-storage means is performed while the current signal is applied to the second charge-storage means.

3. A method according to claim 2 comprising downconverting the current signal, in which the sampling period comprises at least one downconversion period.

4. A method according to claim 3 in which the signal downconversion is quadrature downconversion.

5. A method according to claim 3 in which the signal downconversion is performed at finer than 90°

resolution by;

applying the current signal to the first charge-storage means of each of a plurality of pairs of charge-storage means; and

approximating the voltages derived from charge stored in each first charge-storage means while the current signal is applied to the respective second charge-storage means of each of the plurality of pairs of charge-storage means;

wherein the sampling periods associated with the pairs of charge-storage means are out of phase with respect to each other.

6. A method according to claim 3 in which downconversion of the current signal is performed using switches for selecting one of two input currents of opposite polarity for application to the charge-storage means, the switches arranged to alternate at the downconversion frequency.

7. A method according to claim 6 in which the current signal is inverted at the downconversion frequency.

8. A method according to claim 2 comprising downconverting the digital output signal.

9. A method according to claim 1 in which the approximation comprises comparing the voltage derived from the sampled charge with a reference value and updating the reference value in accordance with the result of the comparison.

10. A method according to claim 1 in which the reference value is a binary number and the updating of the reference value comprises updating successively less significant bits.

11. A method according to claim 1 wherein the sampling comprises at least one of bandpass filtering of the input signal and low-pass filtering of the downconverted input signal.

12. A method according to claim 11 in which the transfer function of the filter comprises notches.

13. A method according to claim 12 wherein the filtering is configured as antialiasing filtering.

14. A method according to claim 1 in which the approximation comprises dithering.

15. An apparatus for performing analogue-to-digital conversion, comprising:

means for converting an input analogue voltage signal to a current signal;

means for storing charge carried by the current signal during a sampling period;

means for performing approximation of a voltage derived from the charge stored during the sampling period by determining one of a successively smaller range of voltage levels which corresponds to the derived voltage; and

means for outputting a digital signal corresponding to the approximated voltage.

16. An apparatus according to claim 15 wherein the approximation means comprises a controller and a register for storing a value corresponding to the approximation.

17. An apparatus according to claim 16 wherein the approximation means further comprises a comparator for comparing a reference voltage corresponding to the stored value with the voltage derived from charge stored by the charge-storage means, the value stored in the register arranged to be updated by the controller in accordance with the result of the comparison.

18. An apparatus according to claim 17 comprising means for downconverting the current signal.

19. An apparatus according to claim 18 in which the signal downconversion is quadrature downconversion.

20. An apparatus according to claim 18 in which the downconversion means comprises at least one switch or an analogue multiplexer.

21. An apparatus according to claim 18 in which the controller is arranged to generate a clock signal for synchronizing the downconversion means with the approximation means.

22. An apparatus according to claim 21 wherein the clock signal is controlled such that the apparatus performs at least one of bandpass filtering of the input signal and low-pass filtering of the downconverted input signal.

23. An apparatus according to claim 22 wherein the filtering is arranged as antialiasing filtering.

24. An apparatus according to claim 15 wherein the charge storage means comprises a capacitor matrix having at least two capacitors arranged in parallel.

25. An apparatus according to claim 24 wherein the capacitors of the matrix have capacitances arranged in a binary-weighted relationship.

26. An apparatus according to claim 25 in which a dithering signal is applied to the sampled input signal using charge stored by one or more of the capacitors in the matrix.

27. An apparatus according to claim 24 comprising a further capacitor matrix, wherein current is arranged to be applied to the further capacitor matrix while approximation is performed of a voltage derived from charge stored by the first capacitor matrix.

28. An apparatus according to claim 27 comprising a plurality of pairs of capacitor matrices, wherein current is arranged to be applied to a first capacitor matrix of each pair in sequence, and approximation of a voltage derived from charge stored by the first capacitor matrix of each pair is arranged to be performed while the current signal is applied to the second capacitor matrix of each pair.

29. An apparatus according to claim 28 in which sampling periods associated with the pairs of capacitor matrices are arranged to be out of phase with respect to each other.

30. An apparatus according to claim 15 in which the current is obtained from the input voltage via one or more transconductance amplifiers.

31. An apparatus according to claim 30 wherein the transconductance amplifier(s) are arranged to produce a differential current output.

32. A radio comprising:

means for receiving a radio signal; and

the apparatus according to claim 15, arranged to perform analogue to digital conversion of the radio signal received by the radio.

33. A mobile phone comprising:

means for receiving a communications signal; and

the apparatus according to claim 15, arranged to perform analogue to digital conversion of the communications signal received by the phone.