# US 2021/0242861 A1 · Receiver with threshold level finder

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- Number: US 2021/0242861 A1
- Document ID: US20210242861A1
- Status: Published application
- Kind: A1
- Application number: 17/301,782
- Filed: 2021-04-14
- Published: 2021-08-05
- Earliest claimed: 2019-11-21
- Assignees: Credo Technology Group Limited
- Applicants: Credo Technology Group Ltd
- Inventors: JUNQING (PHIL) SUN
- Web page: https://patentgrep.com/patent/US20210242861A1

## CPC

- H04L 25/03057: {with a recursive structure (H04L25/03031 takes precedence)}
- H03K 5/082: {with an adaptive threshold}
- H04B 3/04: Control of transmission; Equalising
- H04B 10/695: {Arrangements for optimizing the decision element in the receiver, e.g. by using automatic threshold control}
- H04B 10/6971: {using equalisation}
- H04B 14/023: {using pulse amplitude modulation}
- H04B 14/026: {using pulse time characteristics modulation, e.g. width, position, interval}
- H04L 25/0202: {Channel estimation}
- H04L 25/0214: {of a single coefficient}
- H04L 25/4917: {using multilevel codes}
- H04L 27/01: Equalisers {(baseband equalizers at the transmitter end H04L25/03343; in analogue transmission systems H04B3/04, H04B7/005)}
- H04L 27/02: Amplitude-modulated carrier systems, e.g. using on-off keying; Single sideband or vestigial sideband modulation (H04L27/32 takes precedence)
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)
- H04B: TRANSMISSION

## Abstract

An illustrative receiver includes: a decision element that derives symbol decisions from a slicer input signal; an equalizer that converts a receive signal into the slicer input signal; a summer that combines the symbol decisions with the slicer input signal to produce an error signal; and a level finder that operates on said signals to determine thresholds at which each signal has a given probability of exceeding the threshold. One illustrative level finder circuit includes: a gated comparator and an asymmetric accumulator. The gated comparator asserts a first or a second gated output signal to indicate when an input signal exceeds or falls below a threshold with a programmable condition being met. The asymmetric accumulator adapts the threshold using up steps for assertions of the first gated output signal and down steps for assertions of the second gated output signal, with the up-step size being different than the down-step size.

## Claims

### Claim at position 1

-15. (canceled)

### Claim 16

A receiver that comprises:
a decision element that derives symbol decisions from a slicer input signal;
an equalizer that converts a receive signal into the slicer input signal;
a summer that combines the symbol decisions with the slicer input signal to produce an error signal; and
a level finder that operates on at least one of said receive signal, said slicer input signal, and said error signal, to determine a threshold at which said at least one signal has a given probability of exceeding the threshold.

### Claim 17 (depends on 16)

The receiver of claim 16, wherein each of the decision element, the equalizer, the summer, and a gated comparator component of the level finder, are parallelized to provide concurrent processing paths.

### Claim 18 (depends on 16)

The receiver of claim 16, wherein the probability is subject to a programmable condition being met.

### Claim 19 (depends on 18)

The receiver of claim 18, wherein the programmable condition includes one or more conditions in the list consisting of:
a symbol decision having a given value at a selected offset from a current symbol interval,
a symbol decision not having the given value at the selected offset from the current symbol interval,
a current symbol having a first specified value,
a preceding symbol having a second specified value, and
assertion of one or more matching criterion bypass signals.

### Claim 20 (depends on 16)

The receiver of claim 16, wherein the level finder is a dual level finder.

### Claim 21 (depends on 16)

The receiver of claim 16, wherein the level finder operates on the receive signal to determine upper and lower limits for a range of the receive signal.

### Claim 22 (depends on 21)

The receiver of claim 21, wherein the receiver further comprises control circuitry that uses the upper and lower limits to perform adaptive gain control.

### Claim 23 (depends on 16)

The receiver of claim 16, wherein the level finder operates on the slicer input signal to determine upper and lower eye edges.

### Claim 24 (depends on 23)

The receiver of claim 23, wherein the receiver further comprises control circuitry that uses upper and lower eye edges to set a decision threshold for at least one eye.

### Claim 25 (depends on 23)

The receiver of claim 23, wherein the receiver further comprises control circuitry that detects residual ISI based on the upper and/or lower eye edges and uses the residual ISI to allocate one or more floating taps of the equalizer.

### Claim 26 (depends on 16)

The receiver of claim 16, wherein the level finder operates on the error signal to estimate a bit or symbol error rate.

### Claim 27

A receiver that comprises:
a level finder that operates on a receive signal to determine an upper limit at which the receive signal has a first given probability of exceeding the upper limit and a lower limit at which the receive signal has a second given probability of falling below the lower limit; and
a controller that performs adaptive gain control for the receive signal using the upper and lower limits.

### Claim 28 (depends on 27)

The receiver of claim 27, wherein the first and second given probabilities are equal.

### Claim 29

A receiver that comprises:
an equalizer that converts a receive signal into a slicer input signal;
a decision element that derives symbol decisions from the slicer input signal; and
a level finder that operates on the slicer input signal to determine an upper threshold at which the slicer input signal has a given probability of exceeding the upper threshold for symbol decisions corresponding to a lower edge of an eye.

### Claim 30 (depends on 29)

The receiver of claim 29, wherein the level finder further determines a lower threshold at which the slicer input signal has the given probability of falling below the lower threshold for symbol decisions corresponding to an upper edge of the eye.

### Claim 31 (depends on 30)

The receiver of claim 30, wherein the eye is one of multiple eyes, and wherein the level finder determines upper and lower threshold for each of the multiple eyes.

### Claim 32 (depends on 31)

The receiver of claim 31, further comprising a controller that adjusts a decision threshold for each of the multiple eyes to be midway between the corresponding upper and lower thresholds.

### Claim 33

A method that comprises:
equalizing a receive signal to produce a slicer input signal; and
operating on the receive signal with a level finder to determine an upper limit at which the receive signal has a given probability of exceeding the upper limit and a lower limit at which the receive signal has the given probability of falling below the lower limit.

### Claim 34 (depends on 33)

The method of claim 33, further comprising: using the upper and lower limits to adjust a gain control amplifier for the receive signal.

### Claim 35 (depends on 33)

The method of claim 33, further comprising:
deriving symbol decisions from the slicer input signal; and
operating on the slicer input signal with the level finder to determine an upper threshold at which the slicer input signal has a given probability of exceeding the upper threshold for symbol decisions corresponding to a lower edge of an eye, and to determine a lower threshold at which the slicer input signal has the given probability of falling below the lower threshold for symbol decisions corresponding to an upper edge of the eye.

### Claim 36 (depends on 35)

The method of claim 35, further comprising: using the upper and lower thresholds to adjust a decision threshold for the eye.

### Claim 37 (depends on 33)

The method of claim 33, further comprising:
deriving symbol decisions from the slicer input signal;
combining the symbol decisions with the slicer input signal to produce an error signal; and
operating on the error signal with the level finder to determine an upper threshold at which the error signal has a given probability of exceeding the upper threshold and a lower threshold at which the error signal has a given probability of falling below the lower threshold.

### Claim 38 (depends on 37)

The method of claim 37, further comprising estimating a bit or symbol error rate based at least in part on the upper and lower thresholds.