# US 2018/0323746 A1 · Digital isolator > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2018/0323746 A1 - Document ID: US20180323746A1 - Status: Published application - Kind: A1 - Application number: 16/023,277 - Filed: 2018-06-29 - Published: 2018-11-08 - Earliest claimed: 2012-12-13 - Assignees: Texas Instruments Incorporated - Applicants: Texas Instruments Incorporated - Inventors: Anant Shankar Kamath; Sreeran N. S. - Web page: https://patentgrep.com/patent/US20180323746A1 ## CPC - H03D 3/00: Demodulation of angle-, {frequency- or phase-} modulated oscillations (H03D5/00, H03D9/00, H03D11/00 take precedence) - H04L 25/0268: {with modulation and subsequent demodulation} - H03D: DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER (masers, lasers H01S; circuits capable of acting both as modulator and demodulator H03C; details applicable to both modulators and frequency-changers H03C; demodulating pulses H03K9/00; transforming types of pulse modulation H03K11/00; coding, decoding or code conversion, in general H03M; repeater stations H04B7/14; demodulators adapted for AC systems of digital information transmission H04L27/00; synchronous demodulators adapted for colour television H04N9/66) - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract Several circuits and methods for transferring an input data signal in a digital isolator are disclosed. In an embodiment, the digital isolator includes an isolation element, input circuit, and output circuit. The isolation element includes at least one input node and at least one output node, the input circuit is electronically coupled to the input node and generates modulated differential data signals based on modulating the input data signal on a carrier signal. The input circuit operates using a first supply voltage with respect to a first ground. The output circuit is electronically coupled to the output node to receive the modulated differential data signals, operates using a second supply voltage with respect to a second ground and includes a frequency-shift keying demodulator configured to generate a demodulated data signal in response to detection of presence of the carrier signal. The output circuit further generates an output data signal. ## Claims ### Claim 1 An output circuit for use in an isolation device, the output circuit comprising: a filter circuit including: a filter input; a filter output; a first resistor coupled between the filter input and an output ground node; a capacitor coupled between the filter input and the filter output; and a second resistor coupled between the filter output and an output supply node; and a demodulation circuit coupled to the filter output. ### Claim 2 (depends on 1) The output circuit of claim 1, wherein: the filter input includes first and second filter inputs; the filter output includes first and second filter outputs; the first resistor includes: a third resistor coupled between the first filter input and the output ground node, and a fourth resistor coupled between the second filter input and the output ground node; the capacitor includes: a first capacitor coupled between the first filter input and the first filter output, and a second capacitor coupled between the second filter input and the second filter output; and the second resistor includes: a fifth resistor coupled between the first filter output and the output supply node, and a sixth resistor coupled between the second filter output and the output supply node. ### Claim 3 (depends on 2) The output circuit of claim 2, further comprising: an amplifier coupled between the filter circuit and the demodulation circuit, the amplifier including: a first input coupled to the first filter output; a second input coupled to the second filter output; and an output coupled to the demodulation circuit. ### Claim 4 (depends on 1) The output circuit of claim 1, wherein the demodulation circuit includes a frequency-shift keying (FSK) demodulator. ### Claim 5 (depends on 1) The output circuit of claim 1, wherein the demodulation circuit includes: a switching capacitor coupled between a switch node and the output ground node; a first switch coupled between the switch node and the output ground node; a second switch coupled between the switch node and a compensation node; a pull-up element coupled between the output supply node and the compensation node; an averaging capacitor coupled between the compensation node and the output ground node; and a comparator having a non-inverting input coupled to the compensation node, an inverting input coupled to a reference voltage node, and a demodulation output. ### Claim 6 (depends on 5) The output circuit of claim 5, wherein the pull-up element includes a pull-up resistor. ### Claim 7 (depends on 5) The output circuit of claim 5, wherein the pull-up element includes a current source. ### Claim 8 (depends on 5) The output circuit of claim 5, wherein the demodulation circuit includes: a first reference resistor coupled between the output supply node and the reference voltage node; and a second reference resistor coupled between the reference voltage node and the output ground node. ### Claim 9 (depends on 5) The output circuit of claim 5, wherein the first switch is controlled by a first phase signal based on a modulation signal from the filter output, and the second switch is controlled by a second phase signal complementary to, and non-overlapping with, the first phase signal. ### Claim 10 (depends on 9) The output circuit of claim 9, wherein the demodulation circuit includes a break before make circuit configured to generate the first and second phase signals based on the modulation signal. ### Claim 11 An output circuit for use in an isolation device, the output circuit comprising: a filter circuit including a filter input configured to receive a modulation signal, and a filter output configured to output a filtered modulation signal; and a demodulation circuit including: a switching capacitor coupled between a switch node and an output ground node; a first switch, coupled between the switch node and the output ground node, and controlled by a first phase signal based on the filtered modulation signal; a second switch, coupled between the switch node and a compensation node, and controlled by a second phase signal complementary to, and non-overlapping with, the first phase signal; a pull-up element coupled between an output supply node and the compensation node; an averaging capacitor coupled between the compensation node and the output ground node; and a comparator having a non-inverting input coupled to the compensation node, an inverting input coupled to a reference voltage node, and a demodulation output. ### Claim 12 (depends on 11) The output circuit of claim 11, wherein the pull-up element includes a pull-up resistor. ### Claim 13 (depends on 11) The output circuit of claim 11, wherein the pull-up element includes a current source. ### Claim 14 (depends on 11) The output circuit of claim 11, wherein the demodulation circuit includes: a first reference resistor coupled between the output supply node and the reference voltage node; and a second reference resistor coupled between the reference voltage node and the output ground node. ### Claim 15 (depends on 11) The output circuit of claim 11, wherein the demodulation circuit includes a break before make circuit configured to generate the first and second phase signals based on the filtered modulation signal. ### Claim 16 An isolation device comprising: an input circuit, coupled between an input supply node and an input ground node, and having an input configured to receive an input data signal, and an output configured to output a modulation signal; an isolation element having a first terminal coupled to the output of the input circuit, and a second terminal; a filter circuit including a filter input coupled to the second terminal of the isolation element, and a filter output configured to output a filtered modulation signal; and a demodulation circuit including: a switching capacitor coupled between a switch node and an output ground node isolated from the input ground node; a first switch, coupled between the switch node and the output ground node, and controlled by a first phase signal based on the filtered modulation signal; a second switch, coupled between the switch node and a compensation node, and controlled by a second phase signal complementary to, and non-overlapping with, the first phase signal; a pull-up element coupled between the compensation node and an output supply node isolated from the input supply node; an averaging capacitor coupled between the compensation node and the output ground node; and a comparator having a non-inverting input coupled to the compensation node, an inverting input coupled to a reference voltage node, and a demodulation output. ### Claim 17 (depends on 16) The isolation device of claim 16, wherein the pull-up element includes a pull-up resistor. ### Claim 18 (depends on 16) The isolation device of claim 16, wherein the pull-up element includes a current source. ### Claim 19 (depends on 16) The isolation device of claim 16, wherein the demodulation circuit includes: a first reference resistor coupled between the output supply node and the reference voltage node; and a second reference resistor coupled between the reference voltage node and the output ground node. ### Claim 20 (depends on 16) The isolation device of claim 16, wherein the demodulation circuit includes a break before make circuit configured to generate the first and second phase signals based on the filtered modulation signal.