The configuration of the power supply in multichannel battery-powered
front-ends for biopotential recordings
Alexander C. MettingVanRijn, Anthony P. Kuiper and Cornelis
A. Grimbergen
Academic Medical Center, Medical Physics Department, PO box 22700, 1100 DE
Amsterdam
The Netherlands, e-mail : metting@biosemi.com
- Introduction : The application of a compact, battery-powered
front-end close to the patient, in combination with a fiber-optic or wireless
data link to the signal processing hardware has greatly improved the quality
of biopotential recordings. There are practical advantages if the power supply
circuitry of these front-ends can be designed to work with a battery-pack
with a single output voltage: maximal efficiency, simple connectors, simple
charge circuitry, and minimal size.
- Design : The latest generation front-ends for biopotential recording
systems usually consists of an amplifier and an analog-digital converter per
channel, a logic section (timing and data multiplexing) and a data transmission
circuit (often a fiber-optic LED). The circuitry of such a front-end needs
at least three supply voltages: a dual analog supply and a single digital
supply. Employing a virtual analog ground at the midpoint between the single
digital supply voltage in order to form the analog supply voltages, leads
to three major problems: ground splitter circuits are not unconditionally
stable, the separate analog and digital ground-planes complicate the design
of the motherboard and cabinet, and the low voltages available reduce the
DC input range of the amplifier. The diagram shows a power supply circuit
without these drawbacks. A continuous ground-plane forms both the analog and
the digital ground. Local decoupling to the ground-plane allows the analog
and digital sections to use the same positive supply. The negative supply
is generated by a voltage inverter (switching capacitors). Adding noise to
the recorded signal is prevented by synchronizing the inevitable ripple on
the negative supply with the sampling-rate. Results: The described power supply
was applied in a range of front-ends with 16-bit amplifier/converter modules
designed for +/- 5 V supply. Prototypes in 32, 128, and 256 channel version
were evaluated in clinical practice.
Conclusion : The presented power-supply configuration enables the use
of a single voltage battery pack in high-quality front-ends of biopotential
measurement systems.
Acknowledgment : This research is supported by the Technology Foundation
STW under grant AGN44.3416.
