Sensor Interfaces

PCAP01 Capacitance-to-Digital Conversion Digital Signal Processor

PCapØ1 is a dedicated Capacitance-to-Digital Conversion Digital Signal Processor. Its front end is based on acam‘s patented 4→ principle. This conversion principle offers high resolution at conversion times as short as 2 µs. Customers benefit from outstanding flexibility for optimizing power consumption, resolution and speed.

The PCap01A can be used for grounded single and differential sensors as well as for floating single and differential sensors. With grounded capacitors the stray capacitance inside the chip will be compensated. With floating capacitors, further to the internal stray capacitance, the external stray capacitances as well get compensated. Additionally, the temperature can be measured by means of internal thermistors or external ones (platinum or others). Before loading some firmware to it, the chip is not completely operable. Data will end up in ALU instead of being transferred to processor and/or output. Under this circumstance, we chose to write a combined data sheet covering the hardware aspects as well as handling a very basic firmware called 03.01.xx; this basic or “standard“ firmware calculates the capacitance and resistance ratios and transfers them to the data output ports, still without doing such further possible processing like filtering and linearization. It is provided free of charge with the chip, yet, it needs to be loaded via SPI or I2C.

Dashboard Software

Features

Dedicated ports for precision temperature measurement (with Pt1000 sensors)
Serial interfaces (SPI or I2C compatible)
Single power supply (2.1 to 3.6 V)
RISC processor core using Harvard architecture:
48 x 48 bit RAM Data, 4k x 8 bit volatile program memory, 4k x 8 bit non-volatile (OTP) program memory

Benefits

Digital measuring principle in CMOS technology
Up to 8 capacitances in grounded mode
Up to 4 capacitances in floating mode (potential- free and with zero bias voltage)
Compensation of internal (grounded) and external parasitic capacities (floating)
High resolution: up to 6 aF at 5 Hz and 10 pF base capacitance, or 17 bit resolution at 5 Hz with 100 pF base capacitance and 10 pF excitation
High measurement rate: up to 500 kHz
Extremely low current consumption possible:
Down to 4 µA at 3 Hz with 13.4 bit resolution
High stability with temperature, low offset drift (down to 30 aF per Kelvin), low gain drift when all compensation options are activated.

Applications