Both controller ICs and firmware play important roles in the performance and sensitivity of projected capacitive input (PCI or PCAP) touch solutions. In addition to touch screens of good design and production quality, the selection of controller IC and firmware that measure trace capacitance changes, filter noise, and calculate the exact location of touch events is also vital.
There are different capacitance sensing methods for different projected capacitive ICs. A few capacitance sensing methods are listed below:
- Charge Transfer
- Serial Capacitor Voltage Sensing
- Relaxation Oscillator
- Switching Capacitance with Sigma-Delta Algorithm
Each capacitance sensing method has its advantages and limitations. AMT currently measures capacitance through Serial Capacitor Voltage Sensing.
Considerations in selecting controller ICs are:
- Number of signal inputs should effectively cover target touch screen size
- The report rate should be high enough to be responsive to user operation
- Low power consumption to extend battery life
- Less external components for lower material cost and smaller control board foot print
- Flexible and versatile digital data interface
- Tolerant of variation in touch screens due to material and production process
- Tolerant of variation in operator behavior and operation environment
Since the number of input signals supported by one control IC is limited, some large touch screens will need 2 control ICs to cover all touch screen sensing traces. In order to achieve smooth touch functionality, multi-finger recognition, high linearity, and accuracy, AMT uses different numbers of control ICs on control boards supporting different panel sizes.
If you require touch products, we can offer custom design services for firmware and touch panels. Please contact us for further details.