Wireless transmitter
A magnetic field tolerant amplifier having an amplifier stage, a differential to single-ended output amplifier stage and a first and second delay line. In another embodiment the invention relates to a magnetic gradient cancellation delay line including two coils connected in series at a junction and non-inductively wound to cancel induced currents from magnetic gradient. In another embodiment the invention relates to a patient lead including a flexible circuit substrate having a flexible conductor having distributed impedance. In still yet another embodiment the invention relates to a wireless transceiver system including an RF cancellation delay line; a differential amplifier stage; a differential to single ended output amplifier stage; an A/D converter; an RF transceiver and an antenna.
1. A magnetic and radio frequency field tolerant amplifier for use in a time varying radio frequency field, said time varying radio frequency field having a predetermined frequency, said magnetic and radio frequency field tolerant amplifier comprising:
an amplifier stage, said amplifier stage comprising a pair of differential input terminals and a pair of differential output terminals;
a differential to single ended output amplifier stage, said differential to single ended output amplifier stage comprising a pair of differential input terminals and an output terminal, each of said differential input terminals of said differential to single ended output amplifier stage in electrical communication with a respective differential output terminal of said amplifier stage; and
a delay line having a delay line output terminal and a delay input terminal, said delay line output terminal of said delay line in electrical communication with an input terminal of said pair of differential input terminals of said amplifier stage and said delay line input terminal of said delay line configured for connection to an input signal source, said input signal source having an input signal comprising a signal of interest and a component resulting from effects of a radio frequency field;
wherein said delay line is configured to produce an 180 degree phase shift at the predetermined frequency in the component of said input signal resulting from the effects of the radio frequency field at said delay line output terminal to thereby cancel the component of the input signal resulting from the effects of the radio frequency field having the predetermined frequency and leave the signal of interest of the input signal substantially unaffected.
2. The magnetic and radio frequency field tolerant amplifier of claim 1 further comprising a plurality of amplifier stages, each said amplifier stage comprising a pair of differential input terminals and a pair of differential output terminals, each of said differential output terminals of one of said plurality of amplifier stages in electrical communication with a respective differential input terminal of another of said plurality of amplifier stages through a respective high pass filter.
3. The magnetic and radio frequency field tolerant amplifier of claim 1 wherein said magnetic and radio frequency field tolerant amplifier is to be used in a 64 MHz RF field and wherein each of said first and second delay lines delays said signal by substantially 7.8 nS.
4. The magnetic and radio frequency field tolerant amplifier of claim 1 wherein said input signal source comprises an ECG electrode.
5. The magnetic and radio frequency field tolerant amplifier of claim 1 further comprising a second delay line having a second delay line output terminal and a second delay input terminal, said second delay line output terminal of said second delay line in electrical communication with a second input terminal of said pair of differential input terminals of said amplifier stage and said second delay line input terminal of said second delay line configured for connection to a second input signal source, said second input signal source having a second input signal.
6. The magnetic and radio frequency field tolerant amplifier of claim 1 wherein said delay line comprises a pair of non-inductively wound coils.
7. A method for transmitting physiological data in a time varying radio frequency field, said radio frequency field having a predetermined frequency, the method comprising the steps of:
receiving an input signal comprising a signal of interest and a component resulting from effects of a radio frequency field;
shifting portions of said input signal having the predetermined frequency by 180 degrees using a delay line to form a delayed signal;
providing said delayed signal to an input terminal of a differential amplifier;
providing said input signal to said input terminal of said differential amplifier; and
combining the input signal and the delayed signal at said input terminal of said differential amplifier thereby substantially canceling the component of said input signal resulting from the effects of the radio frequency field having the predetermined frequency and substantially leaving the remaining signal of interest of the input signal unaffected.