A highly flexible waveform generator is desired for applications from neural stimulation to microelectromechanical systems (MEMS) actuator interfaces. The demand for such application includes multi-channel outputs, various waveform shapes, and different output modes.
This thesis presents a high-voltage, high-current arbitrary waveform generator application-specific integrated circuit (ASIC) based on 0.35-µm high-voltage CMOS technology. The chip has 16 independently-controlled biphasic output channels. The output driver is capable of delivering a current up to 5.04 mA with up to 20 V voltage compliance, and a voltage up to 9.45 V with more than 5 mA output current, in current- and voltage-controlled modes, respectively. With an integrated 5k-bit memory, the chip can generate any arbitrary shape of waveform with up to 1 MHz clock frequency. Of particular interest to the neural stimulation applications, the chip can provide adjustable interphase delay period, reverse pulse phase, and charge-balancing phase for safe and efficient stimulation. The charge-balancing approach that shorts all stimulating electrode pairs together after a long sequence of stimulation cycles is also implemented to prevent damages on both electrode and targeted tissue area. The chip has been successfully interfaced and tested with a three-dimensional microfabricated electrode developed in our laboratory for targeted deep brain stimulation. Proof of concept for current steering in vitro in both current and voltage modes, as well as in an in vivo experiment on an anesthetized rabbit, are demonstrated.
For various MEMS applications, a chip with multiple outputs providing both current- and voltage-controlled arbitrary waveforms can accommodate the needs of driving resistive and capacitive devices, as well as multiple sequential waveforms for actuators such as micromotors. An experiment on a silicon carbide flow sensor developed in our laboratory validates the concept of using the chip as a function generator. The chip is configured to supply a 5 mA constant current and a 4.5 mA current pulse to the heater of the flow sensor in order to characterize flow measurement output and response time, respectively.
The foregoing provides an on-chip solution for an arbitrary function generator that can be monolithically fabricated with other circuitry. Based on its configuration, this chip is an ideal solution for various applications, ranging from an on-chip arbitrary function generator to a multi-channel neural stimulator.