# US 2017/0288927 A1 · Signal processing circuits

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- Number: US 2017/0288927 A1
- Document ID: US20170288927A1
- Status: Published application
- Kind: A1
- Application number: 15/443,982
- Filed: 2017-02-27
- Published: 2017-10-05
- Earliest claimed: 2016-04-01
- Assignees: NXP B.V.
- Applicants: NXP B.V.
- Inventors: Nur Engin; Audrey Christine Andrée Cuenin
- Web page: https://patentgrep.com/patent/US20170288927A1

## CPC

- H04L 27/2623: {Reduction thereof by clipping}
- H04L 5/0064: {Rate requirement of the data, e.g. scalable bandwidth, data priority}
- H04L 25/49: using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels {; Baseband coding techniques specific to data transmission systems (spectral shaping H04L25/03828)}
- H04L 27/2601: {Multicarrier modulation systems}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

A signal processing circuit comprising a clip-generation-block. The clip-generation-block is configured to receive an input-signal; and determine a clip-signal that comprises only values of the input-signal that exceed a clipping-threshold. The signal processing circuit also comprises a scaling-block configured to apply a scaling-factor to the clip-signal in order to generate a scaled-clip-signal, wherein the scaling-factor is greater than one; and an adder configured to provide a clipped-signal based on a difference between the scaled-clip-signal and the input signal.

## Claims

### Claim 1

A signal processing circuit comprising:
a clip-generation-block configured to:
receive an input-signal; and
determine a clip-signal that comprises only values of the input-signal that exceed a clipping-threshold;
a scaling-block configured to apply a scaling-factor to the clip-signal in order to generate a scaled-clip-signal, wherein the scaling-factor is greater than one; and
an adder configured to provide a clipped-signal based on a difference between the scaled-clip-signal and the input signal.

### Claim 2 (depends on 1)

The signal processing circuit of claim 1, wherein the scaling-factor comprises a frequency-domain-scaling-factor, which defines a function that varies with frequency.

### Claim 3 (depends on 2)

The signal processing circuit of claim 2, wherein the frequency-domain-scaling-factor comprises a plurality of randomly generated values that are limited to range of values between a maximum-value and a minimum-value.

### Claim 4 (depends on 1)

The signal processing circuit of claim 1, wherein the scaling-factor comprises a time-domain-scaling-factor.

### Claim 5 (depends on 1)

The signal processing circuit of claim 1, wherein the clip-signal comprises:
zero values at instants in time for which the input-signal is less than the clipping-threshold; and
non-zero values at instants in time for which the input-signal is greater than the clipping-threshold.

### Claim 6 (depends on 5)

The signal processing circuit of claim 5, wherein the non-zero values comprise the difference between the input-signal and the clipping-threshold.

### Claim 7 (depends on 1)

The signal processing circuit of claim 1, wherein the scaling-block is configured to multiply the clip-signal by the scaling-factor in order to generate the scaled-clip-signal.

### Claim 8 (depends on 1)

The signal processing circuit of claim 1, further comprising a filter, wherein the filter is configured to attenuate (i) any out-of-band terms in the scaled-clip-signal; and/or (ii) any pilot-subcarriers in the scaled-clip-signal, in order to provide a scaled-filtered-clip-signal; and
wherein the adder is configured to provide the clipped-signal based on a difference between the scaled-filtered-clip-signal and the input-signal.

### Claim 9 (depends on 1)

The signal processing circuit of claim 1, further comprising a feedback-block, which provides a feedback loop to the clip-generation-block and/or the scaling-block, wherein the feedback-block is configured to:
determine a PAPR value and/or a distortion-measure of the clipped-signal; and
selectively provide a feedback-signal to the clip-generation-block and/or the scaling-block based on the PAPR value and/or the distortion-measure; and wherein the clip-generation-block is configured to apply an adjusted-clipping-threshold to the input-signal based on the feedback-signal and/or the scaling-block is configured to apply an adjusted-scaling-factor to the clip-signal based on the feedback-signal.

### Claim 10 (depends on 9)

The signal processing circuit of claim 9, wherein the feedback-block is configured to cause additional iterations of the feedback loop to occur such that different clipping-thresholds and/or different scaling-factors are applied until:
the PAPR value of the clipped-signal reaches a target value;
the distortion-measure of the clipped-signal reaches a target value; or
a predefined number of iterations of the feedback loop have been performed.

### Claim 11 (depends on 9)

The signal processing circuit of claim 9, wherein the feedback-block is configured to, for a second and each subsequent iteration of the feedback loop, determine one or more of the following:
the PAPR value of the clipped-signal, which is based on an input-signal clipped with the adjusted-clipping-threshold;
the distortion-measure of the clipped-signal, which is based on an input-signal clipped with the adjusted-clipping-threshold;
a preceding-PAPR-value, which is based on an input-signal clipped with a preceding-clipping-threshold in an earlier iteration of the feedback loop; and
a preceding-distortion-measure, which is based on an input-signal clipped with a preceding-clipping-threshold in an earlier iteration of the feedback loop.

### Claim 12 (depends on 11)

The signal processing circuit of claim 11, wherein the feedback-block is configured to cause additional iterations of the feedback loop to occur such that different clipping-thresholds are applied and/or different scaling-factors are applied are applied until:
a difference between the PAPR value of the clipped-signal and a preceding-PAPR-value is reduced to a target value; or
a difference between a current-distortion-measure and a preceding-distortion-measure is reduced to a target value.

### Claim 13 (depends on 1)

An OFDM transmitter comprising the signal processing circuit of claim 1.

### Claim 14

A method of processing an input-signal, the method comprising:
determining a clip-signal that comprises only values of the input-signal that exceed a clipping-threshold;
applying a scaling-factor to the clip-signal in order to generate a scaled-clip-signal, wherein the scaling-factor is greater than one; and
providing a clipped-signal based on a difference between the scaled-clip-signal and the input signal.

### Claim 15 (depends on 14)

A non-transitory computer readable media including programming instructions, which when run on by a processor of a computer, causes the computer to perform the method of claim 14.