Automatic lead recognition for implantable medical device

Claim 1

A body-implantable cardiac pacemaker system, comprising: an electronic circuit, wherein said electronic circuit comprises: an excitation circuit coupled to at least one conductor, for applying a sub-threshold symmetrical and bi-phasic voltage pulse along a current path; an impedance measurement circuit, coupled to said at least one conductor and to a second electrode, adapted to measure impedance along said current path during application of said sub-threshold voltage pulse; a comparison circuit, coupled to said impedance measurement circuit and adapted to determine whether said measured impedance lies within a predetermined impedance range, indicating availability of said current path for cardiac pacing; a hermetic enclosure for housing said electronic circuit; a flexible, elongate pacing/sensing lead having at least one conductor therein extending between proximal and distal ends of said lead, said at least one conductor being coupled at said proximal end to said electronic circuit in said hermetic enclosure and coupled near said distal end to a first conductive electrode adapted to be disposed in electrical contact with patient's cardiac tissue; a second electrode, electrically coupled to said electronic circuit in said hermetic enclosure, such that said current path is established extending from said electronic circuit, along said at least one lead to said electrode, through a portion of said patient's body tissue to said second electrode and back to said electronic circuit; Wherein said impedance measurement circuit further comprises: a sampling circuit for obtaining a sample of voltage between said first and second electrodes during said application of said excitation pulse and for obtaining a sample of current between said first and second electrodes during said application of said excitation pulse; an analog-to-digital converter for deriving a digital voltage value corresponding to a logarithm of said sampled voltage and a digital current value corresponding to the logarithm of said sampled current; and an impedance computation circuit for deriving from said digital voltage and current values a digital impedance value corresponding to the logarithm of the impedance between said first and second electrodes during application of said excitation pulse, wherein said voltage pulse is bi-phasic and on the order of 0.26 volts, peak to peak.