IMMS receives iENA silver medal for energy-efficient solutions in integrated circuits

On 16th December 2015 in Ilmenau IMMS was honoured with the iENA silver medal for the development of an „Electronic delay circuit in CMOS technology“ in the context of the iENA trade fair competition for inventors. The work was part of the GreenSense project and will be the basis of further investigations within the ADMONT project.

CMOS thyristor-based delay elements are widely used in integrated circuits such as time-to-digital converters or asynchronous state controllers. Such applications usually require delays in the nanosecond range where these delay elements operate very energy-efficiently. Energy autonomous or energy harvesting systems are applications that require larger delays in the micro- to millisecond range. For this purpose, the power consumption of CMOS thyristor-based delay elements is relatively high. Therefore, the implementation of these elements in energy-autonomous systems has hitherto been impossible.

The inventors Benjamin Saft, Eric Schäfer and Andre Jäger developed a novel low-power CMOS thyristor-based delay element for delay durations in the micro- to millisecond range. Starting from a basic CMOS thyristor delay circuit, they proposed several modifications to reduce the energy/delay ratio by a factor of four: The threshold voltage of the internal CMOS thyristor is raised and a pull-up/down current source is used to increase the delay duration and reduce the influence of subthreshold leakage current on integration time and nonlinearity. A second CMOS thyristor stage increases the steepness of the transition slopes, thereby reducing shunt currents in subsequent stages during the switching event. The circuit was designed and manufactured in a commercial 0.35-µm CMOS process. Measurements were performed on a ring oscillator comprising three instances of the proposed delay elements. By varying the bias currents of the elements, the delay duration can be tuned over more than three decades from 4 µs to 22 ms with excellent linearity.