The trimming requirement becomes more important as process nodes shrink due to the increased variability of analog circuit performance parameters at smaller processes, due to both random and systematic variations in key manufacturing steps. This manifests itself as increasing yield loss when chips with analog circuitry migrate to smaller process nodes since a larger percentage of analog blocks on a chip will not meet design specifications due to variability in process parameters and layout. Examples where trimming is used include automotive and industrial sensors, display controllers, and power management circuits. Trimming is also done to increase the yield of LCD displays by ensuring more uniform performance of the display’s individual pixels.
One-time programmable (OTP) trimming can also be used to match the performance of a system to individual preferences or, for medical applications, health requirements. Examples of preference matching include frequency response of an audio amplifier and screen characteristics of an HDTV. Medical applications include shaping the audio response spectrum of a hearing aid to compensate for the wearer’s hearing losses and adjusting the triggering threshold levels of an implanted pacemaker.
OTP Requirements for Analog Trimming and Calibration
- Small memory area for minimal cost impact
- Low Power (particularly important for wearable and implanted medical devices)
- Field programmable
- High reliability
- HV operation (for LCD drivers and controllers)
DesignWare OTP Features and Benefits
- The smallest embedded field-programmable OTP bit-cell area in the industry to minimize silicon cost
- No additional masks or process steps means no processing cost impact, a critical requirement for consumer electronics devices
- Very low power – operational and standby – to minimize system power drain
- Field updateable without the need for special equipment or programming sources
- Retention time of greater than 10 years up to 125°C for long-term reliability operation
- Support for several HV and BCD process nodes to support consumer and power management applications
Automobiles provide many opportunities for OTP-based trimming and calibration systems that interface with a car’s analog circuits and sensors. Examples where automotive trimming and calibration operations occur include secure vehicle ID (VID) storage, in-car communications, infotainment systems, gas tank vapor and tire pressures, temperatures of various subsystems both outside and under the hood, and positioning of electromechanical devices for brake, steering and other systems.
The examples in the following figure are for trimming and calibration of circuits such as analog amplifiers, ADCs/DACs and sensor conditioning. There are also many other uses for OTP, both in automotive and in other market segments, including microcontrollers, PMICs, and many others.