Voltage overshoot protection

Abstract

A transmission circuit for an RF inductive link, particularly for an implanted device such as a cochlear implant. In a preferred form, the transmission circuit 1 includes a transmitter coil 24 and a damping device, including an auxiliary coil 4 and switch 6 . The switch is operated to close the coil circuit when data zeros are transmitted. This has the advantage of improving modulation depth without placing stress on the RF driver output switches.

1 . An RF transmission circuit for transmitting a data signal, said transmission circuit comprising:
 a transmission coil assembly configured to transmit the data signal across an inductive link; and   a signal generator configured to selectively output high frequency signal pulses to the transmission coil assembly during a series of time spaces to represent data,   wherein the RF transmission circuit is configured to increase an effective inductance of the RF transmission circuit when the signal generator is not outputting the high frequency signal pulses to the transmission coil assembly.   
     
     
         2 . The RF transmission circuit of  claim 1 , wherein:
 the RF transmission circuit is configured to decrease the effective inductance of the RF transmission circuit when the high frequency signal pulses are outputted to the transmission coil assembly.   
     
     
         3 . The RF transmission circuit of  claim 1 , wherein:
 the signal generator is configured to output the high frequency signal pulses to the transmission coil assembly during a time space to represent one digit of a binary digit set.   
     
     
         4 . The RF transmission circuit of  claim 3 , wherein:
 the RF transmission circuit is configured to not output the high frequency signal pulses to the transmission coil assembly during a time space to represent the other digit of the binary digit set.   
     
     
         5 . The RF transmission circuit of  claim 1 , further comprising:
 a damping arrangement configured to be selectively operable during the series of time spaces, wherein the RF transmission circuit operates the damping arrangement during the time spaces when the signal generator is not outputting the high frequency signal pulses to the transmission coil assembly.   
     
     
         6 . The RF transmission circuit of  claim 5 , wherein:
 the RF transmission circuit does not operate the damping arrangement during the time spaces when the signal generator is outputting the high frequency signal pulses to the transmission coil assembly.   
     
     
         7 . The RF transmission circuit of  claim 1 , wherein:
 the transmission coil assembly includes a primary coil and an auxiliary coil,   the RF transmission circuit is configured to inhibit current flow through the auxiliary coil during the time spaces when the signal generator is outputting the high frequency signal pulses to the transmission coil assembly; and   the RF transmission circuit is configured to enable current flow through the auxiliary coil during the time spaces when the signal generator is not outputting the high frequency signal pulses to the transmission coil assembly.   
     
     
         8 . The RF transmission circuit of  claim 1 , wherein:
 the transmission coil assembly includes a primary coil and an auxiliary coil,   the RF transmission circuit is configured to establish an inductance of the auxiliary coil as high capacitive impedance in series with the primary coil during the time spaces when the signal generator is not outputting the high frequency signal pulses to the transmission coil assembly; and   the RF transmission circuit is configured to cancel the established inductance of the auxiliary coil during the time spaces when the signal generator is outputting the high frequency signal pulses to the transmission coil assembly.   
     
     
         9 . The RF transmission circuit of  claim 1 , wherein:
 increasing the effective inductance of the RF transmission circuit when the signal generator is not outputting the high frequency signal pulses to the transmission coil assembly increases a decay time of a ringing waveform existing in the RF transmission circuit from the high frequency signal pulses outputted to the transmission coil assembly.   
     
     
         10 . An apparatus for transmitting a data signal across an inductive link, said apparatus comprising:
 a transmission coil; and   an RF data transmission circuit configured to:
 provide to the transmission coil high frequency signal pulses during selected time spaces of a series of time spaces; and 
 transmit high frequency transmitted signal pulses from the transmission coil during the selected time spaces based on the received high frequency signal pulses having a first power; and 
 reduce a power of any high frequency signal pulses transmitted by the RF transmission circuit resulting from post RF-burst ringing during non-selected time spaces, the post RF-burst ringing resulting from the high frequency signal pulses having a first power received during the selected time spaces. 
   
     
     
         11 . The apparatus of  claim 10 , further comprising:
 a damping arrangement, wherein the RF data transmission circuit is configured to selectively operate the damping arrangement during the non-selected time spaces, thereby reducing the power of any high frequency signal pulses transmitted by the RF transmission circuit resulting from post RF-burst ringing.   
     
     
         12 . The apparatus of  claim 11 , wherein:
 the RF data transmission circuit is configured to selectively increase an effective inductance of the RF data transmission circuit during the non-selected time spaces.   
     
     
         13 . The apparatus of  claim 10 , wherein:
 the RF data transmission circuit is configured to provide the high frequency signal pulses having a first power to the transmission coil during the selected time spaces to represent one digit of a binary digit set.   
     
     
         14 . The apparatus of  claim 10 , wherein:
 the RF data transmission circuit is configured to withhold high frequency signal pulses from the transmission coil during the non-selected time spaces to represent the other digit of the binary digit set.   
     
     
         15 . The apparatus of  claim 11 , wherein:
 the RF data transmission circuit is configured to deactivate the damping arrangement during the selected time spaces.   
     
     
         16 . The apparatus of  claim 10 , wherein:
 the transmission coil assembly includes a primary coil and an auxiliary coil,   the RF transmission circuit is configured to establish an inductance of the auxiliary coil as high capacitive impedance in series with the primary coil during the selected time spaces; and   the RF transmission circuit is configured to cancel the established inductance of the auxiliary coil during the non-selected time spaces.   
     
     
         17 . A medical prosthesis configured to transmit a data signal across a transcutaneous inductive link, said prosthesis comprising:
 an external component including:
 a transmission coil assembly; and 
 an RF data transmission circuit configured to:
 transmit high frequency signal pulses having a first power from the transmission coil during selected time spaces of a series of time spaces; and 
 reduce a power of any high frequency signal pulses transmitted by the RF transmission circuit during non-selected time spaces to below a second power through signal pulse damping; and 
 
   an implantable component including:
 an RF receiver circuit, wherein the second power corresponds to a power below a minimum detection level threshold of the RF receiver circuit, and wherein the first power corresponds to a power above the minimum detection level threshold of the RF receiver circuit. 
   
     
     
         18 . The medical prosthesis of  claim 17 , wherein:
 the signal pulse damping is achieved by increasing the effective inductance of the RF transmission circuit from that of the RF transmission circuit during the selected time spaces.   
     
     
         19 . The medical prosthesis of  claim 17 , wherein:
 the transmission coil assembly includes a primary coil and an auxiliary coil,   the RF transmission circuit is configured to inhibit current flow through the auxiliary coil during the selected time spaces; and   the RF transmission circuit is configured to enable current flow through the auxiliary coil during the non-selected time spaces.   
     
     
         20 . The medical prosthesis of  claim 17 , wherein:
 the transmission coil assembly includes a primary coil and an auxiliary coil,   the RF transmission circuit is configured to establish an inductance of the auxiliary coil as high capacitive impedance in series with the primary coil during the non-selected time spaces; and   the RF transmission circuit is configured to cancel the established inductance of the auxiliary coil during the selected time spaces.