Integrated CMOS Circuits for Optical Communications by M. Ingels and M. Steyaert

This work investigates the feasibility of the mixing of interface circuits for optical communication methods in a typical unmodified digital CMOS course of. This paves the best way for single chip communication methods the place the optical interfaces are built-in on the identical die because the required digital circuitry.

The optical receiver is a key factor within the optical communication hyperlink. On this work, a transimpedance amplifier, which consists of a voltage amplifier with resistive suggestions, is used as the primary stage. In contrast to for many different circuits, the optimum place of its dominant pole is the enter node.

It is usually demonstrated {that a} excessive acquire of the voltage amplifier is primordial to acquire good performances and that this can be obtained via using a number of levels. Noise features are investigated and the conclusion is drawn that the amplifier’s enter capacitance might be smaller than the photodiode’s capacitance for optimum efficiency.

The speculation is put into follow via three built-in optical receivers. They’re realized in 0.8 11m and 0.7 11m CMOS and obtain bitrates from 150 Mb/s as much as 1 Gb/s. The transimpedance-gain of the preamplifier varies from 1 unwell for the 1 Gb/s receiver to 150 unwell at 240 Mb/s. To acquire a commercially enticing answer, it can be crucial that the receiver is suitable with obtainable photodiodes.

The receivers are due to this fact designed for a 1 pF enter impedance (0.8 pF for the 1 Gb/s receiver). They do not require some other exterior part besides for an influence provide decoupling capacitance. The receivers on this work are usually not restricted to the transimpedance amplifier solely.

All of them embrace a post-amplifier that gives additional amplification as much as a full rail-to-rail output swing. Two of the receivers have an built-in computerized biasing circuit primarily based on a duplicate and are so totally autonomous.

A LED-driver is offered to implement the transmitter a part of the optical hyperlink. It’s realized in a typical 0.8 11m CMOS expertise and achieves a bitrate of over 155 Mb/s with a modulation present over 65 rnA. The chance to combine the photodiode on the identical die because the receiver is investigated.

Photodiodes realized in a 2.4 11m CMOS expertise are demonstrated along with a easy 100 Mb/s transimpedance amplifier. It’s proven that the shrinking of the expertise to sub-micron units ends in worse photodiodes.

Nonetheless, with using side-wall junctions and shorter optical wavelengths, medium price optical hyperlinks can nonetheless be realized. Within the final a part of this work, consideration is paid to electrical interference issues that happen when delicate analog circuits are mixed with digital circuitry on the identical die.

The three performers – the noise era, its propagation and the in fluence on delicate circuits – are witnessed and countermeasures are proposed. One in all these is a]lew decoupling technique primarily based on an RLC community.

It gives an enhanced transient response of the facility provide following a disturbance, with out the voltage or energy penalty that’s launched by the standard answer that’s primarily based on a resistor within the provide path.

Another measures, akin to a differential method to single-ended indicators and using guard rings are additionally described. The advantage of the countermeasures are used within the design of the 1 Gb/s receiver.

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