Abstract: A portable electronic neuromuscular stimulator monitors its battery and estimates battery end of life from the number of charging cycles and usage history. The stimulator can also be used with an external adapter to retrieve internally stored data regarding usage. A simplified user interface allows the user to input a level of pain both before and after treatment.

Abstract: The circuit compensates for the difference in the source impedances of signal and reference generating circuits whose outputs are coupled to a sense circuit which loads (draws current from) the signal and reference generating circuits. The signal generating circuit has a source impedance (R.sub.1) and produces either one of two (V.sub.1H or V.sub.1L) output signal levels which is coupled via a first transmission gate having an "ON" impedance R.sub.2 to a first input terminal of the sense circuit. The reference generating circuit has a lower source impedance (R.sub.3) than the signal source and produces an output intermediate the two signal levels which is coupled via a second transmission gate having an "ON" impedance R.sub.4 to a second input terminal of the sense circuit. The reference voltage applied to the second input of the sense circuit is maintained at a predetermined level between the high and low levels of the signal applied to the first input of the sense circuit, by making the sum of R.sub.

Abstract: A memory array of cells produces output signals having either one of a high value (i.e. V.sub.H) or a low value (i.e. V.sub.L). The difference between V.sub.H and V.sub.L is significantly less than the operating voltage (e.g. V.sub.DD) applied across the memory cells and V.sub.H and V.sub.L are offset towards one of the voltage rails (e.g. V.sub.DD or ground ). The memory cell output signals are compared to a reference signal (V.sub.R) derived either from a "dummy" cell or from a memory cell being sensed, where V.sub.R has a value which is less positive than V.sub.H but more positive than V.sub.L. The reference signal and a memory cell signal, are applied to a sense amplifier which is responsive to a relatively small difference between the two signals and which can produce an output (V.sub.O) which is approximately symmetrical with respect to the mid point (V.sub.DD /2) of the operating voltage. A signal (V.sub.H) more positive than V.sub.R causes V.sub.O to be more positive than V.sub.DD /2 and a signal (V.