Capacitive isolated voltage domains
In some embodiments, a receiver circuit is configured to receive a modulated signal from a transmitter that is galvanically isolated from the receiver circuit. The receiver circuit is configured to demodulate the modulated signal by using two comparator circuits that respectively detect the presence or absence of first and second signal states of a carrier signal. Based on the detection of the first and second states, the receiver circuit determines whether the carrier signal is present or absent in the modulated signal to determine a demodulated value of the modulated signal.
1. A device comprising:
a receiver circuit having a first comparator circuit and a second comparator circuit and configured and arranged to
receive a modulated signal, the modulated signal including a binary data signal encoded according to a communication protocol,
provide common mode suppression for current transients, and
demodulate the modulated signal to retrieve the binary data signal by
using the first comparator circuit to detect the absence of a first signal state of the modulated signal,
using the second comparator circuit to detect the absence of a second signal state of the modulated signal, and
determine the absence of a carrier signal in the modulated signal in response to the absence of both the first signal state and the second signal state.
2. The device of claim 1 , further including a transmitter circuit configured and arranged to
generate the modulated signal in response to receiving the binary data signal, and
transmit the modulated signal to the receiver circuit; and wherein:
the receiver circuit is further configured and arranged to receive the modulated signal on a differential pair of signal lines;
the first comparator includes a non-inverting input connected to a first one of the differential pair of signal lines and an inverting input connected to a second one of the differential pair of signal lines; and
the first comparator includes a non-inverting input connected to the second one of the differential pair of signal lines and an inverting input connected to the first one of the differential pair of signal lines.
3. The device of claim 2 , wherein:
the first comparator is configured to indicate an absence of the first state in response to the first one of the differential pair of signal lines having a negative voltage, greater than a negative threshold voltage, with reference to the second one of the differential pair of signal lines; and
the second comparator is configured to indicate an absence of the second state in response to the first one of the differential pair of signal lines having a positive voltage, greater than a positive threshold voltage, with reference to the second one of the differential pair of signal lines.
4. The device of claim 1 , wherein the receiver circuit further comprises a detection circuit configured to detect the absence of the carrier signal based on output signals of the first and second comparators.
5. The device of claim 4 , wherein the detection circuit includes a logical OR gate having a first input connected to an output of the first comparator circuit and a second input connected to an output of the second comparator circuit.
6. The device of claim 5 , wherein the logical OR gate is configured and arranged to:
output a first binary signal, indicating absence of the carrier signal, in response to the first comparator determining the absence of the first signal state and the second comparator determining absence of the second signal state; and
output a second binary signal, representing presence of the carrier signal, in response to either the first comparator determining presence of the first signal state, or the second comparator determining presence of the second signal state.
7. The device of claim 4 , further comprising a filtering circuit connected to an output of the detection circuit.
8. The device of claim 7 , further comprising a driver circuit connected to an output of the filtering circuit.
9. The device of claim 1 , wherein the modulated signal is an on-off key (OOK) modulated signal.
10. The device of claim 1 , further comprising, an isolation circuit, configured and arranged to receive the modulated signal and forward the modulated signal to the receiver circuit.
11. The device of claim 1 , further comprising:
a transmitter circuit configured and arranged to modulate a received data signal to produce a version of the modulated signal having the carrier signal present in response to a first value of the data signal and having the carrier signal absent in response to a second, different value of the data signal, and transmit the version of the modulated signal.
12. The device of claim 11 , further comprising an isolation circuit configured and arranged to receive the transmitted version of the modulated signal from the transmitter circuit and to provide the modulated signal that has capacitive isolation from the transmitter circuit.
13. The device of claim 12 , wherein the transmitter circuit is further configured and arranged to transmit the version of the modulated signal on a differential pair of signals having two signal components and wherein the isolation circuit includes two capacitive isolation paths for a respective and corresponding signal component of the two signal components.
14. The device of claim 11 , wherein the transmitter circuit is further configured and arranged to modulate the data signal with a carrier signal by alternating between two signal states relative to a pair of conductive signal paths, the two signal states including the first signal state and the second signal state.
15. A method, for communication, comprising:
receiving a modulated signal from a differential pair of capacitive-coupled signal lines;
using a first comparator, determining whether a first state of the modulated signal is present;
using a second comparator, determining whether a second state of the modulated signal is present;
in response to either an output of the first comparator or an output of the second comparator indicating that the first or second states of the modulated signal is present, setting a demodulated signal to a first value; and
in response to the output of the first comparator and output of the second comparator indicating that neither of the first or second states of the modulated signal is present, setting the demodulated signal to a second value.
16. The method of claim 15 , wherein the setting of the demodulated signal value to either the first or second values includes generating the demodulated signal using a logical OR gate.
17. The method of claim 15 , wherein:
the determining whether a first state of the modulated signal is present includes determining whether a first one of the differential pair of signal lines has a negative voltage, greater than negative threshold voltage, with reference to a second one of the differential pair of signal lines; and
the determining whether a first state of the modulated signal is present includes determining whether the first one of the differential pair of signal lines has a positive voltage, greater than a positive threshold voltage, with reference to the second one of the differential pair of signal lines.
18. The method of claim 15 , further comprising:
generating the modulated signal from a data signal using a transmitter; and
transmitting the modulated signal on the differential pair of capacitive-coupled signal lines.
19. The method of claim 18 , wherein the generating and transmitting of the modulated signal includes:
in response to the data signal having a first value, transmitting a differential signal that alternates between a first binary differential value and a second binary differential value on the differential pair of signal lines; and
in response to the data signal having a second value, setting the differential pair of signal lines to a same voltage level.
20. An apparatus comprising:
a transmitter circuit configured and arranged to encode a binary data value according to a first communication protocol to produce a modulated signal; and
a receiver circuit configured and arranged to receive the modulated signal from the transmitter and demodulate the modulated signal to retrieve the binary data signal, the receiver circuit including:
a first comparator circuit configured and arranged to detect the absence of a first signal state of the modulated signal,
a second comparator circuit configured and arranged to detect the absence of a second signal state of the modulated signal, and
a detection circuit configured and arranged to demodulate the modulated signal, based on an output of the first comparator and an output of the second comparator, and to output the binary data signal.
21. The apparatus of claim 20 , wherein the detection circuit includes:
a first filter having an input coupled to the output of the first comparator circuit;
a second filter having an input coupled to the output of the second comparator circuit; and
a logic circuit having a first input coupled to an output of the first filter and a second input coupled to an output of the second filter, the logic circuit configured and arranged to determine the absence of a carrier signal in the modulated signal in response to the absence of both the first signal state and the second signal state, and wherein the first and second filters being configured and arranged to pass frequencies of a carrier signal to the inputs of the logic circuit while blocking other frequencies associated with noise.