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Photo: Heinz Nixdorf Institut

Electronic-Photonic Integrated Digital-to-Analogue Converter

In the EPIDAC project, we want to develop novel concepts, which massively improve the performance of digital-to-analogue converters (DACs). The improvement is enabled by implementing the bit paths, the combination of the bit paths, the time-interleaving, and/or the clock in the optical domain. We tackle the issue that e.g. due to linearity and electron velocity boundaries in modern scaled silicon processes, the performances of DACs can not be improved much anymore. The performance of electrical DACs is limited by bandwidth issues, since e.g. for the bit generation, a high numberof paths (e.g. 17 cells for a segmented 6-bit DAC) have to be combined at the output, thereby massively increasing the capacitive parasitics. If the bit paths are combined in the optical domain, we only need a simple one-path transimpedance amplifier (TIA) after the photo diode for the back-transformation into the electronic domain. Hence, higher bandwidth is possible. Moreover, compared to electrical approaches, interleaving can be implemented with lower losses and higher accuracy. The resolution of electrical DACs is limited by timing misalignments. By using externally fed mode-locked laser clock signals with jitter values much lower than what can be achieved with electrical oscillators, the misalignment can be reduced and thereby the resolution increased. Our conceptual pre-studies show that with our electro-optical approach it should be possible to achieve a resolution of 7 effective bits at a bandwidth of 80 GHz. Compared to the state of the art this would increase the resolution by a factor of 4 and the bandwidth by a factor of 2, thereby improving the associated figure of merit by a factor of 8. This will e.g. pave the way for next generation communication systems, measurement devices, and arbitrary waveform generators. For the device realization and electro-optical integration, we apply as basis the EPIC SiGe SG25H4 technology of IHP featuring e.g. a library of optical components as well as BiCMOS transistors with 220 GHz maximum frequency of oscillation. Our key tasks include: System modelling, design and optimisation of optically-assisted DACs including theoretical aspects; development, optimisation and hardware realisation of the required integrated optical components (e.g. photo detectors, segmented modulators, couplers and waveguides) and electrical circuits (e.g. TIAs, modulator drivers, calibration circuits, and depending on the architecture DAC sub-cores); and electro-optical co-integration of the key blocks. EPIDAC combines the complementary competences of Frank Ellinger (h ≥ 28) of TU Dresden in high-frequency circuit design and communications and Lars Zimmermann (h ≥ 20) of IHP in high-speed photonics and electrical-optical integration.

Professor Dr.-Ing. Frank Ellinger
TU Dresden
Institute of Principles of Electrical and Electronic Engineering
Chair of Circuit Design and Network Theory

Professor Dr.-Ing. Lars Zimmermann
TU Berlin
Institute "Hochfrequenz- und Halbleiter-Systemtechnologien"
Field "Hochfrequenztechnik - Photonik"