Configurable Mixed-signal ICs and Asynchronous State Machines Can Optimize Embedded Designs

Introduction 

SoC and MCUs require external circuitry for power management, human interface, or connecting to sensors. As a result, there are almost always comparators, op-amps, level shifters, various logic, and discrete transistors scattered across a design. These SoCs are almost never truly Systems on a Chip. 

In some cases, the support logic needed can be swept up into a low-end FPGA. But usually this is not a cost-saving over discrete components. It is also an inadequate solution since an FPGA cannot address analog or discrete components. For an embedded device, this challenge will be even more pronounced as an MCU or SoC cannot address all the possible sensor, power, and connectivity options.

 

Configurable Mixed-signal ICs

Configurable Mixed-Signal ICs (CMICs) offer a clever solution to these challenges. CMICs are a matrix of analog and digital circuit functions that are configurable through One-Time-Programmable (OTP) Non-Volatile Memory. The pioneer and leader of this new category of devices is Silego Technology. Since introducing CMICs in 2009, Silego has completed over 1,300 customer designs and shipped over 2 billion CMIC devices. Silego’s CMICs offer an Asynchronous State Machine (ASM) and a variety of analog and digital resources that a designer can configure into mixed-signal circuits. Designers can drag and drop these resources and “wire up” their design in a schematic capture tool, or they can emulate the design with the Silego Hardware Development Kit (see Figure 1). When they are satisfied with the design, they can program the CMIC device with the on-board OTP memory.CMICs can be used for a variety of essential mixed-signal functions including motor control, system reset, power sequencing, etc.

 

Figure1: Green PAK Universal Development Kit

 

CMIC Advantages

CMICs offer embedded designers and manufacturers multiple advantages over traditional discretes and analog:

 

Embedded Designs Need Optimized Board Space

A dozen or more components can take up precious space which could be better used for a larger battery or a slimmer form factor.  A CMIC can integrate several components into one tiny product as small as 1.0 x 1.2 mm.  88 percent board reduction is possible.

 

Embedded Designs Need a More Convenient, Faster Way to Innovate & Prototype

Traditional circuit prototyping requires days if not weeks to design a PCB, order components, fabricate the board, assemble, debug and repeat.  CMIC Design, Emulation and Prototyping can be done in just one day. 

 

Embedded Designs Need Lower-Cost Bill of Materials

CMICs have been designed to reduce the bill of materials cost over discrete and analog components.  A recent design profiled on embedded.com highlighted that 1 CMIC part replaced $1.50 of level shift and comparator circuitry with a single $0.35 CMIC. 

 

Embedded Developers Want a Confidential Design That Is Hard to Copy

The custom circuitry inside a CMIC is as secure as a full custom IC and only the designer or its designated ODM and supply chain partners can procure it.

 

No static power & no code ASM vs. Low Power MCU for embedded applications

Portable systems often use low power microcontrollers to address their challenges with size and battery life. Silego’s CMICs with ASM offer an alternative solution. The following comparisons illustrate design tradeoffs between microcontrollers and CMIC’s ASM.

 

Handling MCU code

The ASM in Silego’s 5th generation GreenPAK CMIC contains 8 states and 24 possible decisions. The ASM represents an MCU program with up to 24 IF...THEN statements. When the 8 State ASM capabilities are considered together with hardware input and output circuits, the CMIC may be represented as being roughly equivalent to about 100 lines of standard C code written for common 8 and 16 bit MCUs.A CMIC ASM is event-driven and does not operate with a clock. As such, when there are no events, the ASM stays in one state and consumes no static power. Thus, applications with limited input cycles can operate at leakage current power consumption well into the single-digit nanoamps of average current consumption at room temperature. 

 

Handing embedded control problems

Silego has modernized the ASM, mitigating the well-known hazard and race conditions, the programming/configuration headaches, while retaining all the inherent low-power, low-latency benefits for simple (up to 8 states) embedded control problems that would require less than 100 lines of code.  

 

Overkill microcontrollers vs. CMIC ASM value

Microcontrollers are often inefficient in size and power. It is quite common to find MCUs designed into applications where less than 1% of the MCU horsepower will ever be used. CMIC’s ASM is well suited to simple embedded control applications, especially ultra-lower power applications (see Figure 2).

 

Figure 2: GreenPAK Block Diagram with I2C

 

Interrupt latency (ns vs. us)

An important benchmark for microcontrollers is how short is the time from an external interrupt signal until the core is executing the first instruction of the interrupt service routine (ISR), the so-called interrupt latency. MCU interrupt latency is usually measured at around 5 to 10us.  

An ASM equivalent of interrupt latency is measured in nanoseconds. If the CMIC is operating at 5V power supply, the latency is a maximum of only 50ns. 

 

VDD variation

A CMIC ASM works over a wide voltage range. A properly designed ASM is guaranteed hazard and race condition free because each ASM signal path is guaranteed by signal length and gate count. Thus, as the VDD changes, so does the propagation delay. However, the propagation delays are all matched and thus performance is guaranteed.

Microcontrollers, on the other hand, are clocked with signals that are not correlated well with VDD. As the VDD changes, the MCU propagation delays change and since the timing doesn’t change, the timing margins are soon compromised. 

 

Crash vs. no crash

Design and system flaws that can cause a microcontroller to crash include: poorly written software, timing issues, miscalculations of interrupt latency, running out of stack memory, memory leakages, and accidental writes in program memory. Silego’s ASM is configured in hardware with NVM bits, has no timing issues, latency measured in ns, no stack memory, no ability for memory leakage, and no ability to unintentionally overwrite program memory, and is therefore inherently more robust with VDD noise and brownouts.

 

No Code GUI based tools vs. typical MCU tools

A CMIC ASM is configured using the GreenPAK Designer development environment. The software is an easy to use schematic capture editor that can reduce the typical MCU tool learning curve from months to Silego’s GPAK learning curve of a few days (see Figures 3).

 

Figure 3: CMIC Asynchronous State Machine Software

 

CMIC size vs. low-power MCUs

Without all the complexity of the MCU architecture, the CMIC is usually smaller.  If a CMIC product can perform the control function, then it is also usually the smallest programmable option on the market.

 

CMICs Make Embedded Design Easier and Products Better

In summary, the tiny CMIC with the 8 state ASM can take on a variety of embedded control applications that would formerly have been the exclusive domain of microcontrollers. The easily configured ASM brings key advantages of ultra-fast state transitions, leakage level static current consumption, robust design, and supply voltage tolerance important for IoT, portable, and embedded applications.  In addition, CMICs offer many benefits that will allow embedded designers’ to make products more profitable. 

 

About the Authors

Mike Noonen works as the Vice President of Sales and Business Development at Silego Technology. He is particularly skilled in the field of semiconductors; product development, management and marketing; and mixed signals. He earned his Director's Consortium Certificate for Corporate Governance at Dartmouth College - The Tuck School of Business at Dartmouth located in Hanover, New Hampshire, US. He is also a Bachelor's Degree holder in Electrical Engineering at Colorado State University.

John McDonald works as a Vice President of Marketing at Silego Technology, a company that designs the world's highest efficiency power switches, tiny programmable mixed-signal ICs, and 32.768 kHz clocks. Silego ships billions of components into the most demanding consumer applications including notebooks, tablets, smartphones, wearables, etc. John is an expert in the field of semiconductors, integrated circuits, as well as mixed-signals.

Nathan John works at Silego Technology as the Marketing Director. He is also specialized in semiconductors, integrated circuits and product marketing. He earned his Master of Business Administration in Finance and Marketing at Arizona State University and his Bachelor's Degree in Computer Science at the University of California, San Diego.

 

This article originally appeared in the Bodo’s Power Systems magazine.