By Sowmyan Rajagopalan, Founder and CTO, Thalia Design Automation
FD-SOI is receiving significant traction with analog designers, but analog IP reuse often equates to tough choices. Porting chips from bulk to FD-SOI or creating new chips on FD-SOI means making decisions on porting existing bulk IP or starting from scratch.
To invest the time and resources in reusing an analog IP requires a judgement call on the potential returns from the market and the time it takes to get the IP to that market to generate revenue is key – if a competitor’s project hits the market first, then the potential returns are greatly diminished. There is also a need to understand the differences in process technologies and the impact those differences have on the efficient reuse of analog IPs. All this means that the demands on resources and time are high.
A typical decision fork faced by many companies is whether to design new IPs, or if they should instead build a portfolio of analog IPs. Given the opportunity cost, availability of resources, time and resources needed for each option means that doing both is a difficult option.
Both have their advantages; designing new IPs allows companies to branch out and address new sectors or markets. New IPs often demand higher revenues and engages in-house designers as the work, by its nature, is more innovative and challenging. On the other hand, building a portfolio of analog IPs allows companies to expand in an existing market, bringing stabilisation and strengthening revenues from existing product sectors.
But why should you have to choose when there’s a third option?
It is difficult for a company to drive both options internally – not least because there’s a paucity of good analog designers in the market, and the opportunity cost is simply too high. However, the good news is that firms like Thalia have the specialist expertise and toolsets required build a portfolio of analog IP, saving time and investment while in-house designers focus on new IP design.
Over the last 18 months, there has been a rapid uptake of FD-SOI process technologies. With production at foundries such as GlobalFoundries and Samsung now in full swing, more and more analog designers are reaping the benefits of FD-SOI.
At Thalia we’ve been at the forefront of some of these changes, having worked with multiple customers on projects that use FD-SOI technology.More & more analog designers are reaping the benefits of #FDSOI. At Thalia we’ve been at the forefront of some of these changes, having worked with multiple customers on projects that use FD-SOI technology. - @Thalia_IP_Reuse CTO Click To Tweet
This figure contrasts the structures of traditional bulk planar and SOI type transistors. The main difference is the inclusion of a buried oxide layer that isolates the channel of the transistor from the bulk silicon of the substrate. This results in a very thin, controllable channel structure, with much lower leakage currents being ‘lost’ into the device substrate than traditional alternatives.
This in turn improves two key figures of merit for the device. First, standby power consumption is dramatically reduced. Second, the threshold voltage is much more predictable and controllable – yields are improved, and power/performance tradeoffs via voltage scaling are more easily enabled.
The penalty is that FD-SOI transistors are generally not so fast. But one other feature of the technology – particularly important for mixed signal and analog designs – allows smart designers to mitigate this effect. Biasing the body structure at a different voltage to the source enables the designer to trade speed for power: a reverse bias increases the threshold voltage of the device, making it slower, but reducing leakage current; conversely, forward biasing reduces the threshold voltage, increasing the speed of the device, at the cost of power.
Thalia has worked on a number of projects that utilize SOI technologies. A recent RF front end for Bluetooth Low Energy (BLE), for example, used exactly the techniques I have outlined above. We migrated an entire subsystem design, composed of around 30 blocks (including ADCs, PLLs, mixers, amplifiers and power controllers), to a 28nm Samsung FD-SOI process.
The circuit was verified for compliance with design specifications. Design changes were implemented to ‘nudge’ the design to meet the requirements. And we made full use of the body biasing techniques I have already outlined. We used reverse body biasing to keep leakage as low as possible in parts of the circuit in which speed was not a factor; and, where speed was a key requirement, implemented forward gate biasing to increase performance.
We’re expecting increasing numbers of customers to start moving their analog and mixed signal designs to SOI technologies in the coming months and years. The process is not without its challenges: but with an intimate knowledge of circuit design and optimization, and of the subtleties of the processes themselves, there are substantial advantages to be reaped.
A large part of the effort involved with migrating an IP from one technology to another is involved with qualifying the IP in the target technology; if a block doesn’t meet the requirements of the target technology, it won’t function. Identifying the cause of this – the technology characteristics that cause it – and then addressing them is key to a successful outcome.
Whenever a key specification is not being met in the target technology, we have to determine which process technology or circuit characteristic is causing this. By using our automated technology analyser, we can take a design-centric approach to analyse and compare base and target technologies to see where the process technologies are similar and where they differ the most. The technology analyser considers both first and second order effects including FT, gm/id, Vdsats among others. Using this technology, we can identify which characteristics differ between the origin and target technologies.
With traditional methods, identifying differences in characteristics would be time consuming, but our technology analyzer gives a clear and rapid identification of the issues, allowing us to fix any mis-matched topologies and achieve a functioning result in the target technology.
Our platform comprises three elements – Technology, Methodology and Design Expertise. Using this trifecta, we have been able to deliver IPs in different technologies, nodes and with improved characteristics.
Tech analyzer: Using a design-centric approach, the platform addresses key first and second order effects of process technologies and extracts and compares characteristics between base and target technologies to provide the user with clear inputs on how similar the technologies are.
Automated schematic porting: Taking the inputs from the analyzer and generates a circuit in the target technology. This circuit can then be verified for response and characteristics.
Design enabler: Once the circuit design for the target technology is correct, the design enabler and our team of experienced designers can nudge the circuit back into specification.
Layout migration: The final stage is focussed on putting together the base layout framework which is then expanding on by our experienced layout designers.
We are Thalia Design Automation. I founded Thalia in 2011, with the aim of improving the efficiency and process cost of analog circuit design and to rollout an analog IP reuse platform. We’ve worked with vendors, numerous foundries and different nodes and have design centres in Germany and India with our headquarters in the UK. We have successfully rolled out an analog IP reuse platform that combines smart technology, a smart methodology and our smart and experienced resources to streamline the IP reuse process.
In doing all this, Thalia regularly provides customers with a time saving of around 50% compared to a traditional circuit redesign. And as I stated at the beginning of this article, achieving a faster time to market is key to maximizing revenues from any IP.