Multiple frequency bio-impedance measurement system
First Claim
1. A multiple frequency system for the noninvasive examination of living tissue by measuring the impedance of the tissue at any one of a plurality of frequencies, said system being adapted to be connected to the living tissue to be examined by electrode means and comprising:
- signal generator means for generating a stable frequency output signal which can be selectively varied over a range of frequencies;
electrode drive means for applying a substantially constant current examination signal derived from said stable frequency output signal to said electrode means;
current control means connected between said signal generator means and said electrode drive means for regulating the current level of said constant current examination signal; and
signal processor means for monitoring an impedance signal generated in response to said constant current examination signal and generating an impedance signal representative of the impedance of said tissue, said signal processor means being coupled to said current control means to complete a current control feedback loop for maintaining the current level of said constant current examination signal.
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Abstract
The multiple frequency impedance measurement system of the present invention permits noninvasive examination of living tissue at any one of a plurality of frequencies. Precise frequency control is provided by a phase locked loop (PLL) circuit which is adjustable among at least a plurality of frequencies by locking the loop to the output signal generated by a voltage controlled oscillator (VCO) divided by a selectable divisor. By selecting the divisor of the output signal of the VCO, the frequency is changed and, due to the use of a PLL circuit, each selected frequency is stably maintained. Electrodes connecting the circuit to tissue to be monitored are driven by a high-Q filter and buffer amplifier which convert the square wave output from a voltage controlled clipper circuit to a sine wave signal. The clipper circuit receives the output signal from the VCO and is part of a feedback loop which maintains a constant examination current for the system. By monitoring the examination current via a precision resistor, a current reference signal is generated and used in the feedback loop to maintain the current at a substantially constant but selectable level. The reference signal is also used to drive a resistance synchronous detector and a reactance synchronous detector to derive resistance and reactance signals, respectively, which are representative of the resistance and reactance of the tissue at the selected measuring frequency. The resistance and reactance signals are displayed via a shared digital display which is switched between the two signals.
213 Citations
19 Claims
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1. A multiple frequency system for the noninvasive examination of living tissue by measuring the impedance of the tissue at any one of a plurality of frequencies, said system being adapted to be connected to the living tissue to be examined by electrode means and comprising:
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signal generator means for generating a stable frequency output signal which can be selectively varied over a range of frequencies; electrode drive means for applying a substantially constant current examination signal derived from said stable frequency output signal to said electrode means; current control means connected between said signal generator means and said electrode drive means for regulating the current level of said constant current examination signal; and signal processor means for monitoring an impedance signal generated in response to said constant current examination signal and generating an impedance signal representative of the impedance of said tissue, said signal processor means being coupled to said current control means to complete a current control feedback loop for maintaining the current level of said constant current examination signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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Specification