In this blog, I want to highlight a seemingly impossible design problem that Cactus Semiconductor took on with an electronic solution that will save and improve countless lives.
Many people need to take prescription drugs to improve their blood pressure, lower their cholesterol, and many other reasons to improve their health. Some seemingly non-life critical conditions appear not to be a serious threat if we miss a dose or two; however, many people (especially the elderly) forget to take a dose of maybe take a double dose because they forgot that they already swallowed that pill an hour ago—that could lead to a serious overdose condition or if the behavior is chronic, your kidneys could fail or you could have a heart attack.
Andrew Kelly, Cactus Semiconductor IC/Systems architect behind the podium and to his left is Jonathan Withrington, IC Design Manager, Proteus Digital Health (Image courtesy of Loretta Taranovich)
- There are 187 Americans requiring Prescriptions
- 20% to 30% of Medication Prescriptions are never filled
- 50% of all Medications are not taken as prescribed
- 30% to 50% of treatment failures are due to non-adherence
- 125,000 annual deaths are due to non-adherence
The Proteus Discover device
The Proteus Discover system contains ingestible sensors, a small wearable sensor patch, an application on a mobile device and a provider portal.
Shown here is a summary from Proteus that reveals a chronic problem of a patient not taking their pills on time, skipping doses or doubling up on doses. (Image courtesy of Proteus)
The system is FDA-cleared, monitors and tracks taking of medication (Precise Medication, Dosage, Timing, & Frequency Data), provides medication-taking data to prescribers, and improves engagement with the patient's Healthcare Team.
The pill sensor design challenges
- First, how do to generate power when designers cannot use a traditional battery because of the size and toxicity of standard batteries?
- Next, implementing Passive/Wireless Charging, which needs a prohibitive inductor size and low signal strength.
- The device will be swallowed and then enter into a human stomach, so the solution needs to be non-toxic as well as non-harmful
- Signal Propagation inside a human stomach will be have a high attenuation and variability
- The product swallowed will need programmability with an individual serial number for each pill and in addition, every pill must be accurately and reliably recognized
- Accurate data integrity is critical
- The system needs to be manufacturable and support high production volumes
- Continuity of supply must be maintained with capability of long-term production
- The cost needs be insignificant as compared to the medication
- Functionality and performance improvements in future design revisions as well as no size increase in the future
Other than these problems—the design should be easy!
The sensor ASIC challenges
- Power Supply
- Very Low Voltage
- High Impedance
- Very Low Capacity – Orders of magnitude less than Hearing Aid designs
- Highly Variable Voltage and Impedance
- Must Support Complex Communication Protocol
- Very Small ASIC (1 mm2 )
The Power supply
All materials used are safely ingestible in small doses (Common doses of materials in the ASIC and battery, we frequently get in our food: bananas have silicon, cashews have copper, fish have magnesium, and celery contains cellulose). The ASIC is small and the soluble disk, about the size of a grain of salt, ensures mechanical safety, and finally, the tiny power supply capacity ensures electrical safety. (Image courtesy of Cactus Semiconductor)
(Image courtesy of Cactus Semiconductor)
Signal Propagation: : Use an encoded, on-off-key data transmission technique; shorting the supply would interrupt the Electric Field; and the modulated signal would need to be detected by the patch electronics.
Programmability : To include one-time programmable (OTP) Memory in ASIC including: serial number (> 1 Billion unique values), communication mode selections, analog calibration constants, can be programmed at wafer probe, capability to be read at power-up.
Power supply : Needs to be a custom low voltage/low power design.
Complex Communication Protocol : To include sync and preamble fields, handle multiple carrier rates; have multiple programmable bit rates and packet lengths; and multiple digital encoding schemes.
Improved supply and noise rejection
Including a unique power supply scheme; with a high-precision oscillator; and multi-parameter calibration.
ASIC Qualification Tests
Rigorous ASIC Test Release Procedure
Cactus Semiconductor has the unique advantages of having an ISO-Certified Quality Management System, a fully qualified Supply Chain, a qualified/mature Process Technology, and a best-practices design approach.
Wafer Scale Processing by Cactus Semiconductor : with ASIC Fabrication, ASIC Test, OTP Programming, and Metal Deposition
Automated Saw, Pick & Place by Proteus
Automated Disk Punch & Die Attach by Proteus
Cactus Semiconductor managed to design a complex IC layout that would meet very difficult design needs (Image courtesy of Cactus Semiconductor)
The final ingestible sensor design achieved their critical specs of a power supply current under 20 uA, Low VCAP voltage drop, Small broadcast switch resistance, a high oscillator calibration resolution, and high oscillator stability at low voltages. Data integrity remained high and battery life was maximized. A die of 1 mm2 was achieved as well.
Nice design for such a challenging problem!
1 “An Proteus Ingestible Sensor for Measuring Medication Adherence”, IEEE Transactions on Biomedical Engineering, Vol. 62, No. 1, (2015), Hooman Hafezi, Timothy L. Robertson, Member, IEEE, Greg D. Moon,Kit-Yee Au-Yeung, Mark J. Zdeblick, Member, IEEE, and George M. Savage