- 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.