Development of ASIC for battery powered stylus

A leading component provider of human interface solutions wanted to develop an ultra low power IC. The battery operated product was designed as a replacement for an earlier passive device to reduce cost and complexity. Customer had made a prototype using discrete ICs for proof of concept for performance however power consumption of the ASIC was the key challenge. Finding a silicon partner was a challenge for the customer as several vendors did not deem the power budget as practically achievable.

Challenges:

• Ultra low power requirement to ensure battery life of 24 months operating of a small battery
• Realization of high voltage functions needed for the device to communicate with the environment
• Varied functions requiring different skills,viz, ultra low power switched cap DC-Dc regulators, complex power on sequencing, sensor interface and ADC were needed
• Selecting a process technology providing optimal cost and functionality tradeoff
• Complex on chip sensors with calibration
• A detailed understanding of the complete system
• Aggressive time to market schedule < 12 months from project start to volume production
• Total input cap on sensor pins had to be kept very low (< 2pF) for proper sensor operation calling for careful attention to package and ESD protection circuit design
• High voltage ESD solution with minimal parasitic capacitance to ensure low power

Solutions:

• Cosmic understood the complete system a key step to ensure the modules specs were derived clearly. All module specs were derived with system implications in mind. Specifications for sensor interfaces were derived with complete understanding of the system issues along with the customer.
• Cosmic provided the key innovation in power consumption by using an innovative solution to generation of a high voltage function on chip which required 5X lower power than conventional technique.
• A 20V 0.18um low leakage process with triple gate oxide for 20V from Global Foundries was selected as it provided all the voltage elements – transistors and capacitors without compromising the area or power of the core voltage components
• Availability of wide IP portfolio enabled choosing the right charge pump, PLL and ADC IPs from existing portfolio to use thus minimizing risk and development time
• In house test development expertise ensured design for test to be embedded in the chip which ensured smooth test development without surprises
• Cosmic’s package test and foundry partnerships and control of chip development operations is now ensuring regular production shipments

Impact:

• Cosmic delivered final solution meeting the system functionality and power budget leading to smooth release to mass production of the end product
• Part is in mass production

Development of Microphone Preamp

Our customer wanted to develop a MEMS microphone preamp ASIC. The sensor process variations were limiting the yield of his microphone solution and the existing ASICs provided no mechanism to change the parameters of the ASIC to remove the non idealities of the sensor. The Customer came to Cosmic looking for an ASIC solution to calibrate the sensor variations and maintain constant preamp output for a given external input despite variation in the sensor due to manufacturing process. Cosmic understood the requirements, selected the appropriate technology node and provided a solution to meet the stringent requirements.

Challenges:

• Ultra low noise requirement was the main challenge in the design across audio band without using any external components
• Realization of high voltage functions to bias the sensor while keeping the power consumption under control was another challenging requirement
• Ultra low power consumption < 150uA was an important requirement as mics are usually used in hand held, battery operated devices like mobile phones, digital still cameras etc.
• A robust mechanism to calibrate the sensor & preamp was a key requirement and the main motivation for the new ASIC
• Wide supply range of operation from 1.4V to 3.3V
• Immunity to supply noise - > 70dB PSRR
• Maintaining output DC level in a system without DC feedback

Solutions:

• Cosmic chose appropriate technology node providing the right cost/performance trade off
• Challenging noise specification and low distortion were met by choosing appropriate amplifier architecture
• A charge pump and power on reset circuit were integrated based on power management IP portfolio.

Impact:

• Cosmic has developed the ASIC solution for microphone and it is in mass production with more than 5MU shipped.