Multiple frequency bio-impedance measurement system
US5063937A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 12, 1990 |
| Grant date | Nov 12, 1991 |
| Priority date | — |
| Expiry date | Sep 12, 2010 |
Classification
- Technology area (CPC A)Human Necessities
- CPC primaryA61B5/0535
- WIPO fieldMedical technology
- WIPO sectorInstruments
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…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.