Method and apparatus for full duplex signaling across a transformer
View Patent ↗Simultaneous bi-directional communication of digital signals across an isolation barrier, such as a pulse transformer, is presented. On the pimary side of the barrier, a voltage driver drives a digital transmit data stream, that is encoded to be DC balanced in both current and voltage domains, across the barrier. On the secondary side, an impedance switching circuit modulates the load impedance of the voltage driver in accordance with a digital receive data stream. The modulation of the load impedance is detected on the primary side by sampling the sourced current of the voltage driver to extract the digital receive data. The voltage driver may be sampled at predictable points in time when the current it is sourcing is primarily dependent upon the load impedance of the secondary side. Alternatively, the magnetizing inductance current of the isolation barrier can be subtracted from the current sourced due to the known transmit data.
1. An apparatus comprising:
an transformer having a primary side and a secondary side;
a first circuit coupled to said primary side of said transformer and to a source of transmit data, said first circuit configured to encode said transmit data into a transmit data stream that has DC balanced current and DC balanced voltage characteristics, said first circuit further configured to drive said transmit data stream across said transformer; and
a second circuit coupled to said secondary side of said transformer and to a source of receive data, said second circuit configured to detect said transmit data stream and to modulate load impedance on said secondary side based on said receive data;
wherein said first circuit is further configured to provide source current to satisfy said load impedance and to isolate magnetizing inductance current of said transformer from said sourced current.
2. The apparatus of claim 1 , wherein said transformer is an element of an isolation barrier.
3. The apparatus of claim 1 , wherein said first circuit comprises one or more DC-balanced encoders.
4. The apparatus of claim 3 , wherein said one or more DC-balanced encoders comprises a Manchester encoder.
5. The apparatus of claim 3 , wherein said one or more DC-balanced encoders comprises a 3B/4B encoder.
6. The apparatus of claim 1 , wherein said first circuit comprises a current sensor configured to detect said impedance modulation.
7. The apparatus of claim 6 , wherein said current sensor is configured to sample said sourced current when said magnetizing inductance current of said transformer is near a minimum magnitude.
8. The apparatus of claim 6 , wherein said first circuit further comprises a current feedback loop configured to cancel said magnetizing inductance current of said transformer.
9. The apparatus of claim 1 , wherein said second circuit comprises an impedance circuit with a plurality of switchable impedance values.
10. The apparatus of claim 9 , wherein said impedance circuit comprises:
a first impedance;
a switch in series with said first impedance; and
a second impedance in parallel with said first impedance and said switch.
11. The apparatus of claim 10 , wherein said first impedance and said second impedance comprise a first resistor and a second resistor, respectively.
12. The apparatus of claim 10 , wherein said switch comprises a FET transistor.
13. An apparatus comprising:
an transformer having a primary side and a secondary side;
a first circuit coupled to said primary side of said transformer and to a source of transmit data, said first circuit configured to encode said transmit data into a transmit data stream that has DC balanced current and DC balanced voltage characteristics, said first circuit further configured to drive said transmit data stream across said transformer, said first circuit further configured to isolate magnetizing inductance current of said transformer from a source current, said first circuit further configured with a current sensor to detect changes in values of load impedance on said secondary side by measuring said source current; and
a second circuit coupled to said secondary side of said transformer and to a receive data source, said second circuit configured to detect said transmit data stream and to modulate said load impedance on said secondary side based on said receive data.
14. The apparatus of claim 13 , wherein said current sensor is configured to sample said sourced current when said magnetizing inductance current of said transformer is near a minimum magnitude.
15. The apparatus of claim 13 , wherein said first circuit further comprises a current feedback loop configured to cancel said magnetizing inductance current of said transformer.
16. An apparatus comprising:
an transformer having a primary side and a secondary side;
a first circuit coupled to said primary side of said transformer and to a source of transmit data, said first circuit configured to encode said transmit data into a transmit data stream that has DC balanced current and DC balanced voltage characteristics, said first circuit further configured to drive said transmit data stream across said transformer, wherein said first circuit is further configured to measure changes in load impedance on said secondary side of said transformer; and
a second circuit coupled to said secondary side of said transformer and to a receive data source, said second circuit configured in detect said transmit data stream; said second circuit further configured with a load impedance circuit having a switch controlled by said receive data for modulating said load impedance between a plurality of values.
17. The apparatus of claim 16 , wherein said load impedance circuit comprises:
a first impedance circuit coupled in series with said switch; and
a second impedance circuit coupled in parallel with said first impedance circuit and said switch.
18. The apparatus of claim 17 , wherein said first impedance circuit and said second impedance circuit comprise a first resistor and a second resistor, respectively.
19. The apparatus of claim 16 , wherein said switch comprises a FET transistor.