# US 10,312,889 B2 · Clock signal generator

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- Number: US 10,312,889 B2
- Document ID: US10312889B2
- Status: Granted
- Kind: B2
- Application number: 15/605,541
- Filed: 2017-05-25
- Published: 2018-05-31
- Granted: 2019-06-04
- Earliest claimed: 2016-11-30
- Assignees: STMicroelectronics S.r.l.
- Applicants: STMicroelectronics SA
- Inventors: Denis Pache; Stephane Le Tual; Hanae Zegmout
- Web page: https://patentgrep.com/patent/US10312889B2

## CPC

- H03K 3/42: by the use, as active elements, of opto-electronic devices, i.e. light-emitting and photoelectric devices electrically- or optically-coupled
- G06F 1/105: {in which the distribution is at least partially optical}
- H03K 3/36: by the use, as active elements, of semiconductors, not otherwise provided for
- H03M 1/1255: {Synchronisation of the sampling frequency or phase to the input frequency or phase}
- H10F 30/00: Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors
- 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)
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)
- H03M: CODING; DECODING; CODE CONVERSION IN GENERAL (using fluidic means F15C4/00; optical analogue/digital converters G02F7/00; coding, decoding or code conversion, specially adapted for particular applications, see the relevant subclasses, e.g. G01D, G01R, G06F, G06T, G09G, G10L, G11B, G11C, H04B, H04L, H04M, H04N; ciphering or deciphering for cryptography or other purposes involving the need for secrecy G09C)
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION

## Abstract

The present disclosure relates to a device for generating a clock signal including a first photoresistor coupling a capacitive output node to a node receiving a first potential. A second photoresistor couples the capacitive node to a node receiving a second potential. The first and second photoresistors receive the same optical pulses of a mode-locked laser at instants in time offset by a first delay.

## Claims

### Claim 1

A device for generating a clock signal, comprising:
a first photoresistor coupling a capacitive output node to a node configured to receive a first potential; and
a second photoresistor coupling the capacitive node to a node configured to receive a second potential; and
wherein the first and second photoresistors are configured to receive optical pulses at instants in time that are offset by a first delay to generate the clock signal on the capacitive node;
a first optical splitter configured to transmit the optical pulses to first and second waveguides having different lengths; wherein each photoresistor includes a germanium region on an extension of a flared portion of a silicon core of one of the first and second waveguides.

### Claim 2 (depends on 1)

The device according to claim 1, wherein the first delay is substantially between 20 and 100 ps.

### Claim 3 (depends on 1)

The device according to claim 1, wherein the product of a value of the capacitance of the capacitive node and a resistance value of each photoresistor in an on state is less than substantially 3 ps.

### Claim 4 (depends on 1)

The device according to claim 1, wherein each photoresistor has during receipt of the optical pulses a resistance value in the on state of less than substantially 50 ohms.

### Claim 5 (depends on 1)

The device according to claim 1, wherein a center wavelength of the optical pulses is substantially between 1.3 and 1.8 μm, and each photoresistor comprises a germanium region doped to less than substantially 5*1016 atoms/cm3 and including two contact regions formed in the germanium region and separated by a distance of substantially between 3 and 9 μm.

### Claim 6 (depends on 1)

The device according to claim 1, wherein the product of a value of the capacitance of the capacitive node and a resistance value of each photoresistor in the off state is greater than substantially 2 ns.

### Claim 7

A device for generating a clock signal, comprising:
first and second clock circuits configured to receive optical pulses at instants in time that are offset by a first delay, each of the first and second clock circuits including first and second photoresistors and the photoresistors of the first and second clock circuits being coupled to first and second capacitive output nodes, respectively, and the first and second clock circuits configured generate first and second electronic signals on the first and second capacitive output nodes responsive to the received optical pulses; and
a flip-flop circuit having first and second inputs coupled to the first and second capacitive nodes, respectively, and having an output, the flip-flop circuit configured to generate the clock signal on an output responsive to the first and second electronic signals, and wherein the flip-flop circuit includes a differential-type logic circuit including:
first and second current mode logic cells, each current mode logic cell including first and second differential inputs and a differential output, the first current mode logic cell including its first differential inputs coupled to receive the first electronic signal, its second differential inputs coupled to the differential outputs of the second current mode logic cell, and its differential outputs coupled to the first differential inputs of the second current mode logic cell, the second differential inputs of the second current mode logic signal coupled to receive the second electronic signal.

### Claim 8 (depends on 7)

The device according to claim 7 further comprising:
a first waveguide having a first length coupled to the first clock circuit;
a second waveguide having a second length that is different than the first length coupled to the second clock circuit; and
a first optical splitter configured to receive a pulsed laser signal and to split the pulsed laser signal to thereby transmit the optical pulses through the first and second waveguides to the first and second clock circuits.

### Claim 9 (depends on 8)

The device according to claim 8, where each of the first and second clock circuits further comprises:
a third waveguide having a third length coupled to the corresponding first photoresistor;
a fourth waveguide having a fourth length that is different than the third length coupled to the corresponding second photoresistor; and
a second optical splitter configured to receive the optical pulses from the corresponding first or second waveguide and to split the optical pulses to thereby transmit the optical pulses through the third and fourth waveguides to the corresponding first and second photoresistors.

### Claim 10 (depends on 9)

The device according to claim 9, wherein the third and fourth lengths of the third and fourth waveguides, respectively, provide a second delay of substantially between 20 and 100 ps for the optical pulses provided to the first and second photoresistors.

### Claim 11 (depends on 7)

The device according to claim 7, wherein the first delay is substantially between 100 and 1000 ps.

### Claim 12 (depends on 7)

The device according to claim 7, wherein the differential-type logic circuit comprises an RS flip-flop circuit.

### Claim 13 (depends on 7)

The device according to claim 7, wherein each photoresistor comprises a germanium region having contact regions formed in the germanium region, the contact regions being spaced apart by a distance that is substantially equal to between 3 and 9 μm.

### Claim 14

A method of generating a clock signal, comprising:
receiving a first laser signal including a plurality of pulses, wherein a center wavelength of the optical pulses is substantially between 1.3 and 1.8 μm;
splitting the first laser signal to generate second and third laser signals;
delaying each of the second and third laser signals by different amounts to generate second and third delayed laser signals;
providing the delayed second laser signal to a first photoresistor coupled to a first capacitive node, the first photoresistor including a germanium region doped to less than substantially 5*1016 atoms/cm3 and including two contact regions formed in the germanium region and separated by a distance of substantially between 3 and 9 μm;
providing the delayed third laser signal to a second photoresistor coupled to the first capacitive node, the second photoresistor including a germanium region doped to less than substantially 5*1016 atoms/cm3 and including two contact regions formed in the germanium region and separated by a distance of substantially between 3 and 9 μm; and
generating a first clock signal on the first capacitive node in response to variations in the values of the first and second photoresistors caused by the second and third laser signals.

### Claim 15 (depends on 14)

The method of claim 14, wherein delaying each of the second and third laser signals by different amounts comprises propagating the second and third laser signals through first and second waveguides having different lengths.

### Claim 16 (depends on 14)

The method of claim 14 further comprising:
generating a pulsed laser signal;
splitting the pulsed laser signal to provide a first pulsed laser signal and a second pulsed laser signal;
delaying the first pulsed laser signal by a first delay to provide the first laser signal;
delaying the second pulsed laser signal by a second delay to provide a fourth laser signal, the second delay being different than the first delay;
splitting the fourth laser signal to generate fifth and sixth laser signals;
delaying each of the fifth and sixth laser signals by different amounts to generate fifth and sixth delayed laser signals;
providing the delayed fifth laser signal to a third photoresistor coupled to a second capacitive node;
providing the delayed sixth laser signal to a fourth photoresistor coupled to the second capacitive node;
generating a second clock signal on the second capacitive node in response to variations in the values of the third and fourth photoresistors caused by the provided delayed fifth and sixth laser signals; and
generating an output clock signal responsive to the first and second clock signals.