Wireless power transfer
A power receiver ( 105 ) comprises an input circuit ( 107, 503 ) with a receiver coil ( 107 ) extracting power from a power transfer signal generated by a power transmitter ( 101 ). A variable load ( 511 ) applies a modulation loading to the input circuit ( 107, 503 ) and a data transmitter ( 509 ) transmit data symbols to the power transmitter ( 101 ) by load modulating the power transfer signal during communication time intervals interspersed by non-communication time intervals during which no data symbols are transmitted. The data symbols are represented by modulation loading patterns and the data transmitter ( 509 ) is arranged to control the variable load ( 511 ) to repeatedly change the modulation loading during non-communication time intervals. The approach may provide improved communication and power transfer operation, and may in particular reduce transients, e.g. in the supply voltage provided to a load of the power receiver ( 105 ).
1 . A power receiver comprising:
an input circuit,
wherein the input circuit comprises a receiver coil,
wherein the receiver coil is arranged to extract power from a power transfer signal;
a variable load coupled to the input circuit, wherein the variable load is arranged to apply a modulation loading to the input circuit; and
a data transmitter circuit,
wherein the data transmitter circuit is arranged to transmit data symbols to a power transmitter by load modulating the power transfer signal during communication time intervals,
wherein the communication time intervals are interspersed by non-communication time intervals,
wherein no data symbols are transmitted by the data transmitter circuit during the non-communication time intervals,
wherein the data transmitter circuit is arranged to vary the variable load so as to apply a modulation loading pattern for each data symbol transmitted during the communication time intervals,
wherein each possible data symbol value is represented by a different modulation loading pattern,
wherein the data transmitter circuit is arranged to control the variable load so as to apply a repeating loading variation pattern during the non-communication time intervals,
wherein a maximum absolute difference between a cross-correlation of the repeating loading variation pattern and the modulation sequence data sequences and a reference correlation is no more than 50% of a maximum absolute difference between an auto-correlation of the modulation sequence data sequences and the reference correlation,
wherein the reference correlation is an average correlation between the modulation sequence data sequences and a random sequence.
2 . The power receiver of claim 1 , wherein a difference between an average modulation loading during the non-communication time intervals and an average modulation loading during the communication time intervals differs by less than 10% of a maximum modulation loading change during the communication time intervals.
3 . The power receiver of claim 1 , wherein an average time between modulation loading changes during the non-communication time interval is no less than 50% of an average time between modulation loading changes during the communication time interval.
4 . The power receiver of claim 1 , claim wherein the modulation loading pattern for each possible data symbol value comprises at least two different loading values.
5 . The power receiver of claim 1 , wherein the modulation loading pattern for each possible data symbol value comprises a load modulation chip sequence of at least five load modulation chips.
6 . The power receiver of claim 5 , wherein the modulation loading during non-communication time intervals does not include a modulation loading pattern corresponding to any load modulation chip sequence.
7 . The power receiver of claim 5 , wherein each chip of the load modulation chip sequence is represented by a modulation loading transition.
8 . The power receiver of claim 5 , wherein a number of modulation loading changes during a load modulation chip sequence duration in the non-communication time intervals is no less than a maximum number of modulation loading changes in the load modulation chip sequences.
9 . The power receiver of claim 1 , wherein the repeating loading variation pattern is a periodically changed between two modulation loadings.
10 . The power receiver of claim 1 , wherein the data transmitter circuit is arranged to control the variable load so as to not include any modulation loading pattern representing a data symbol during non-communication time intervals.
11 . The power receiver of claim 1 , wherein the data transmitter circuit is arranged to switch the variable load between two modulation loading values.
12 . A method comprising:
extracting power from a power transfer signal;
transmitting data symbols to the power transmitter by load modulating the power transfer signal during communication time intervals,
wherein the communication time intervals that are interspersed by non-communication time intervals,
wherein no data symbols are transmitted during the non-communication time intervals;
varying the variable load to so as apply a modulation loading pattern for each data symbol transmitted during the communication time intervals,
wherein each possible data symbol value is represented by a different modulation loading pattern; and
controlling the variable load so as to apply a repeating loading variation pattern during the non-communication time intervals,
wherein a maximum absolute difference between a cross-correlation of the repeating loading variation pattern and the modulation sequence data sequences and a reference correlation is no more than 50% of a maximum absolute difference between an auto-correlation of the modulation sequence data sequences and the reference correlation,
wherein the reference correlation is an average correlation between the modulation sequence data sequences and a random sequence.
13 . The method of claim 12 , wherein a difference between an average modulation loading during the non-communication time intervals and an average modulation loading during the communication time intervals differs by less than 10% of a maximum modulation loading change during the communication time intervals.
14 . The method of claim 12 , wherein an average time between modulation loading changes during the non-communication time interval is no less than 50% of an average time between modulation loading changes during the communication time interval.
15 . The method of claim 12 , wherein the modulation loading pattern for each possible data symbol value comprises at least two different loading values.
16 . The method of claim 12 , wherein the modulation loading pattern for each possible data symbol value comprises a load modulation chip sequence of at least five load modulation chips.
17 . The method of claim 16 , wherein the modulation loading during non-communication time intervals does not include a modulation loading pattern corresponding to any load modulation chip sequence.
18 . The method of claim 16 , wherein each chip of the load modulation chip sequence is represented by a modulation loading transition.
19 . The method of claim 16 , wherein a number of modulation loading changes during a load modulation chip sequence duration in the non-communication time intervals is no less than a maximum number of modulation loading changes in the load modulation chip sequences.
20 . The method of claim 12 , wherein the repeating loading variation pattern is periodically changed between two modulation loadings.
21 . The method of claim 12 , further comprising controlling the variable load so as to not include any modulation loading pattern representing a data symbol during non-communication time intervals.
22 . The method of claim 12 , further comprising switching the variable load between two modulation loading values.
23 . A computer program stored on a non-transitory medium, wherein the computer program when executed on a processor performs the method as claimed in claim 13 .