Method and apparatus for detection of load impedance modulation in a transformer circuit
A method and apparatus for detection of load impedance modulation as a result of communication of data from the secondary to the primary side of a transformer are presented. The load impedance on the secondary of the transformer barrier is modulated differentially using data to be communicated across the barrier. A detection circuit on the primary side isolates the load current from the magnetizing current in the primary. The load current is subsequently integrated over two consecutive Manchester periods and the integrated value from the first Manchester period is compared against that of the second period thereby recovering the receive data.
1. An apparatus for detecting a load impedance in a transformer comprising:
a transformer having a primary side and a secondary side;
a first circuit component coupled to said secondary side of said transformer configured to differentially modulate a load impedance on said secondary side of said transformer by:
obtaining a data stream for communication from said secondary side to said primary side of said transformer;
converting said data stream to a differential bitstream; and
modulating said load impedance on said secondary side using said differential bitstream; and
a second circuit coupled to said primary side of said transformer configured to detect said modulated load impedance by differentially integrating a load current on said primary side of said transformer.
2. The apparatus of claim 1 , wherein said second circuit is configured to isolate said load current from a total current on said primary side of said transformer by canceling a magnetizing current component of said total current.
3. The apparatus of claim 1 , wherein said second circuit is configured
to:
measure an output of a voltage driver on said primary side, wherein said output is a voltage equivalent of an absolute value of said load current;
generate an error signal between said load current and an average of said load current;
generate an integrated output voltage by integrating said error signal; and compare said integrated output voltage to a fixed value at specific time intervals to generate discrete values corresponding to said modulated load impedance.
4. The apparatus of claim 3 , wherein said second circuit is configured to generate said error signal by:
converting said voltage equivalent to said load current;
generating an average of said equivalent voltage;
converting said average of said voltage equivalent to said average of said load current;
and
generating said error signal by subtracting said average of said load current from said load current.
5. A method for detecting a load impedance in a transformer having a primary side and a secondary side comprising:
obtaining a data stream for communicating from said secondary side to said primary side of said transformer;
converting said data stream to a differential bitstream;
modulating said load impedance on said secondary side of said transformer using said differential bitstream; and
detecting said modulated load impedance by differentially integrating a load current on said primary side of said transformer.
6. The method of claim 5 , wherein said load current is isolated from a total current on said primary side of said transformer by canceling a magnetizing current.
7. The method of claim 6 , wherein said differentially integrating said load current comprises:
measuring an output of a voltage driver on said primary side of said transformer, wherein said output is a voltage equivalent of absolute value of said load current;
generating an error signal between said load current and an average load current;
generating an integrated output voltage by integrating said error signal;
and
comparing said integrated output voltage to a fixed value at specific time intervals to generate discrete values corresponding to said modulated load impedance.
8. The method of claim 7 , wherein said generating an error signal comprises:
converting said voltage equivalent to said load current;
generating an average of said voltage equivalent;
converting said average of said voltage equivalent to said average load current;
and
generating said error signal by subtracting said average load current from said load current.