ANALOG TO DIGITAL CONVERTER

Abstract

The invention relates to an analog-to-digital converter (ADC). The objective of the invention to have an analog-to-digital converter with the capability of non-equidistant sample time spacing and minimizing energy consumption will be solved by an apparatus comprising a sigma-delta modulator and a sample-time-counter, both controlled by a sample clock, a next-sample-time-computation unit configured to compute a sample-time-counter value when a next digital output sample is requested, a sample-computation-trigger unit connected to the next-sample-time-computation unit configured to compare an actual sample-time-counter value with the sample-time-counter value when the next digital output sample is requested and to trigger a computation unit for calculating a next digital sample when requested and by powering off the sigma-delta modulator in intervals where its delivered samples are not used for any computed decimator output sample. The objective is also solved by a method using the aforementioned analog-to-digital converter.

Claims

1. An analog-to-digital converter comprising a sigma-delta modulator and a sample-time-counter, both controlled by a sample clock, a next-sample-time computation unit configured to compute a sample-time-counter value when a next digital output sample is requested, a sample-computation-trigger unit connected to the next-sample-time computation unit configured to compare an actual sample-time-counter value with the sample-time-counter value when the next digital output sample is requested and to trigger a computation unit for calculating a next digital sample when requested.

2. An analog-to-digital converter according to claim 1, wherein the computation unit comprises an output-compute-counter unit, a sample buffer and an output-sample accumulator, whereas the output-compute-counter unit and output-sample accumulator are triggered in dependence of a difference between the actual sample-time-counter value and the next sample-time-counter value, whereas the output-sample accumulator is configured to compute digital output samples in dependence of a filter response read sample by sample from a filter coefficient memory and an accumulation of said samples after multiplication with the related digital output value of the sigma-delta modulator read from the buffer at certain values of the sample-time-counter.

3. An analog-to-digital converter according to claim 1, wherein a sigma-delta modulator power control unit powers on or off the sigma-delta modulator according to a next digital sample request.

4. An analog-to-digital converter according to claim 1, wherein an RF power control unit powers on or off the RF receiver chain or a part of the RF receiver chain according to a next digital sample request.

5. An analog-to-digital converter according to claim 1, wherein the sigma-delta modulator is a single-bit or a multi-bit and/or a continuous-time or discrete-time and/or a bandpass or baseband sigma-delta modulator.

6. An analog-to-digital converter according to claim 1, wherein the next-sample-time-computation unit is activated by a request format consisting in delivering N samples of equidistant spacing T starting at time point t.

7. An analog-to-digital converter according to claim 1, wherein the sample-computation-trigger unit powers on the sigma-delta modulator if the difference of the actual sample-time-counter value and the sample-time-counter value when the next digital output sample is requested falls below a threshold value.

8. An analog-to-digital converter according to claim 1, wherein the sample-computation-trigger unit triggers the computation of the next digital output sample if the actual sample-time-counter value and the sample-time-counter value when the next digital output sample is requested matches.

9. An analog-to-digital converter according to claim 1, wherein the sample-time-counter value is a current sampling time plus an offset K.

10. An analog-to-digital converter according to claim 1, wherein an one-time larger offset is used to skip a portion of the signal, in which case the sigma-delta modulator is powered off.

11. An analog-to-digital converter according to claim 1, wherein a shape of the filter is varied by a change of coefficients stored in the filter coefficient memory and a length of the filter.

12. A method for converting an analog signal into a digital signal using the analog-to-digital converter according to claim 1, wherein the method comprising the following steps: using a sigma-delta modulator to produce a quantized, noise-shaped signal at a large sampling frequency, delivering output samples at requested output sample time positions by computing weighted sums over appropriate ranges of input samples according to the filter length, optionally powering off the sigma-delta modulator when no filtered sample is requested in an off-period.

13. The method for converting an analog signal into a digital signal according to claim 12, wherein the method comprises the step that an receiver radio frequency path, or part of a receiver radio frequency path prior to the sigma-delta modulator are powered off.

14. The method for converting an analog signal into a digital signal according to claim 12, wherein a receiver requests the filtered samples equidistantly spaced or non-equidistantly spaced.

Description

[0034] The appended drawing shows

[0035] FIG. 1 Schematical drawing of a timeline, with on- and off-periods and where samples are requested in the on-period and no samples are requested in the off-period;

[0036] FIG. 2 An analog-to digital converter with the inventive extension of the computation unit;

[0037] FIG. 3 An analog-to digital converter of FIG. 2 with a detailed view of the computation unit;

[0038] FIG. 4 An analog-to digital converter with an optional RF path for power control and an optional pre-decimation filter to minimize overall decimation filtering complexity and power consumption.

[0039] FIG. 1 shows a timeline with on- and off-periods, whereas samples are requested in the on-period. In the off-period no samples are requested. In such off-periods it is possible to power off the sigma-delta modulator 1 and other components of the RF side, because they are not needed when no samples are requested. This results in saving energy and a reduction in the overall power consumption. With the inventive analog-to-digital converter it is possible to request output samples at any time, meaning at an arbitrary point in time whenever it is desired. An advantage is that this is not restricted to equidistant time positions as with standard A/D converters.

[0040] FIG. 2 shows an analog-to-digital converter 16 which receives a continuous-time analog signal 14 and delivers a discrete-time digital signal 13. A sample clock 3 controls the sigma-delta modulator 1 and a sample time counter 2. The samples are put out by the computation unit 17 whenever the comparison of the actual sample-time-counter value with the sample-time-counter value when the next sample is requested matches, meaning when the delta of the two values is zero. So, the sigma-delta modulator power control 7 turns on the sigma-delta modulator 1, if the delta of the two values falls below a filter length of the computation unit 17, and if the values match, it triggers the computation of the next output sample.

[0041] FIG. 3 shows the analog-to-digital converter 16 with a possible embodiment of the computation unit 17. FIG. 3 shows an analog-to-digital converter 16 which receives a continuous-time analog signal 14 and delivers a discrete-time digital signal 13. A sample clock 3 controls the sigma-delta modulator 1 and a sample time counter 2. Furthermore, the sigma-delta modulator can be connected to an optional pre-decimation filter 18. Inserting a simple pre-decimation filter 18 allows minimizing the overall implementation complexity and power consumption of the decimation filter as a whole. The digital output values 12 of the sigma-delta modulator 1 are stored in a sample buffer 4, under control of the sample time counter 2. A sample computation request 15 asks for digital output samples 13 to be computed at certain values of the sample-time-counter 2. A simple format of such a request consists in delivering N samples of equidistant spacing T time ticks of the sample clock. More complex, implementation specific request formats are possible, e.g., to skip the cyclic prefix in OFDM, or to obtain a non-integer sampling frequency ratio. The next-sample-time-computation unit 5 computes the sample-time-counter value when the next output sample is requested. For equidistant sampling, the next sample time is the current sample time plus an offset K. In OFDM, a one-time larger offset, e.g., NCP*K, may be used to skip the cyclic prefix, in which case the sigma-delta converter may get powered off. The sample-computation-trigger unit 6 serves two purposes, both based upon comparing the actual sample-time-counter value with the sample-time-counter value when the next sample is requested: If the delta of the two values falls below the filter length, it requests the sigma-delta modulator power control 7 to turn on the sigma-delta modulator 1, and if the values match, it triggers computation of the next output sample. The actual output sample computation consists in reading the filter impulse response sample by sample from the filter coefficient memory 10 and accumulating 9 after multiplication 11 with the related sample value read from the buffer 4, given that each output sample is a weighted sum over a set of input samples stored in the sample buffer 4.

[0042] The sigma-delta modulator 1 could be single-bit or multi-bit, continuous-time or discrete-time, baseband or bandpass sampling of any order. Compared to related art, the proposed solution requires only a small amount of logic to implement the required functionality, it is able to perform the required functionality at very low power consumption, it offers versatile use, and it supports simple variation of the filter shape by change of coefficients and length of the computation unit 17.

[0043] FIG. 4 shows another embodiment of the invention. The analog-to-digital converter can additionally comprise an optional RF path power control unit which is triggered by the sample-computation trigger unit 6 and is used to power on or off the entire RF receive path, or parts of the RF receive path.

REFERENCE SIGNS

[0044] 1 sigma-delta modulator [0045] 2 sample-time-counter [0046] 3 sample clock [0047] 4 sample buffer [0048] 5 next-sample-time-computation unit [0049] 6 sample-computation-trigger unit [0050] 7 sigma-delta modulator power control unit [0051] 8 output-compute-counter unit [0052] 9 output-sample accumulator [0053] 10 filter coefficient memory [0054] 11 multiplication [0055] 12 digital output value of the sigma-delta modulator [0056] 13 digital output samples [0057] 14 analog input signal [0058] 15 sample computation request [0059] 16 analog-to-digital converter [0060] 17 computation unit [0061] 18 pre-decimation filter [0062] 19 RF path power control unit