Glossary
AN66308 - CY8CMBR2044 CapSense® Design Guide, Doc. No. 001-66308 Rev. *F
47
Modulation IDAC is a programmable constant current source, whose output is controlled (ON/OFF) by the
sigma-delta modulator output in a CSD block to maintain the AMUXBUS voltage at V
REF
. The average
current supplied by this IDAC is equal to the average current drawn out by the sensor capacitor.
Mutual-Capacitance
Capacitance associated with an electrode (say TX) with respect to another electrode (say RX) is known
as mutual capacitance.
Negative Noise Threshold
A threshold used to differentiate usual noise from the spurious signals appearing in negative direction.
This parameter is used in conjunction with the Low Baseline Reset parameter.
Baseline is updated to track the change in the Raw Count as long as the Raw Count stays within
Negative Noise Threshold, that is, the difference between Baseline and Raw count (Baseline
– Raw
count) is less than Negative Noise Threshold.
Scenarios that may trigger such spurious signals in a negative direction include: a finger on the sensor on
power-up, removal of a metal object placed near the sensor, removing a liquid-tolerant CapSense-
enabled product from the water; and other sudden environmental changes.
Noise (CapSense Noise)
The variation in the Raw Count when a sensor is in the OFF state (no touch), measured as peak-to-peak
counts.
Noise Threshold
A parameter used to differentiate signal from noise for a sensor. If Raw Count
– Baseline is greater than
Noise Threshold, it indicates a likely valid signal. If the difference is less than Noise Threshold, Raw
Count contains nothing but noise.
Overlay
A non-conductive material, such as plastic and glass, which covers the capacitive sensors and acts as a
touch-surface. The PCB with the sensors is directly placed under the overlay or is connected through
springs. The casing for a product often becomes the overlay.
Parasitic Capacitance (C
P
)
Parasitic capacitance is the intrinsic capacitance of the sensor electrode contributed by PCB trace,
sensor pad, vias, and air gap. It is unwanted because it reduces the sensitivity of CSD.
Proximity Sensor
A sensor that can detect the presence of nearby objects without any physical contact.
Radial Slider
A widget consisting of more than one sensor arranged in a specific circular fashion to detect the physical
position of a finger.
Raw Count
The unprocessed digital count output of the CapSense hardware block that represents the physical
capacitance of the sensor.
Refresh Interval
The time between two consecutive scans of a sensor.
Scan Resolution
Resolution (in bits) of the Raw Count produced by the CSD block.
