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Description
The paper presents a Dual Use Driver (DUDE) that is a component designed for the “Demonstrator ASIC for Radiation-Tolerant Transmitter” in 28nm (DART28) and is developed in R&D programme on technologies for future experiments. The driver operates at 25.6Gbps and it allows to drive either 100Ω transmission lines and optical ring modulators in a Photonics Integrated Circuit. The driver includes configurable pre-emphasis. The device will allow to demonstrate the feasibility of wavelength division multiplexing optical links operating with bandwidths in excess of 100Gbps per fiber that are capable of sustaining total ionizing radiation doses up to 10MGy.
Summary (500 words)
The circuit described here is designed in the framework of the Strategic R&D Programme on Technologies for Future Experiments in the Work Package 6 (WP6) - High Speed Links (HSL). The objective of WP6 HSL is to demonstrate the feasibility of wavelength division multiplexing (WDM) optical links operating at bandwidths in excess of 100 Gbps per fiber while being capable of sustaining radiation with Total Ionizing Doses (TID) approaching 10 MGy radiation.
Dual Use Driver (DUDE) is a part of the Demonstrator ASIC for Radiation-Tolerant Transmitter in 28 nm (DART28). The first prototype operates at 25.6 Gbps per lane and uses NRZ signaling. The paper will present a driver prototype which is an intermediary stage between the serializer and the Photonics Integrated Circuit (PIC). PIC includes components as ring modulators, PIN-diodes and waveguides. The whole system is aim to work in the high radiation zone.
DUDE is a multipurpose, modular unit which is capable of driving both 100 Ω transmission lines and ring modulators. This approach allows not only the Silicon Photonics (SiPh) co-integration but it extends the testability of the system especially in a high radiation environment.
The DUDE is a pseudo-differential driver with two symmetric complementary outputs for anode and cathode. The output stage is segmented to enable adjustment of the output current which is desirable in order to compensate Process-Voltage-Temperature variations and to adapt to various loads. The DUDE consists of the 29 segments in total which can be enabled and programmed individually.
Both complementary outputs can be programmed in one of the modes of operation:
- 100 Ω transmission line driver
- reduced swing driver
- full swing CMOS driver
A particular challenge of this design is the driving of the SiPh ring modulator with the low voltages compatible with the supply voltage of the 28 nm CMOS technology. To overcome this limitation (and to maximize the driving amplitude) the ring modulator is driven pseudo-differentially on both the anode and cathode terminals. This, however, might lead to the PN-junction of the ring modulator being forward biased, which must to be avoided. To prevent that, the driver was designed to produce reduced (and programmable) amplitude signal swing on the anode terminal.
The DUDE includes a pre-emphasis circuit which is able to compensate for channel bandwidth limitations in order to minimize intersymbol interference (ISI). Two modes of pre-emphasis are implemented:
- Two-tap Feed-Forward Equalization (bit-level pre-emphasis);
- Edge pre-emphasis.
Feed-Forward Equalization is implemented by the pre- and the post-cursor drivers in both complementary outputs. Their driving strength is individually programmable, allowing for optimal equalization of bandwidth-limited channels. Edge pre-emphasis can be used to additionally improve rise and fall times at the output nodes of the driver by providing increased current to the load during signal transitions. Its strength can be controlled by means of the current impulse duration and the amplitude of additional current supplied.
The paper will present the architecture of the system, implementation details, functionality of the various modes of operations and performance studies.
