at42qt1481 ATMEL Corporation, at42qt1481 Datasheet - Page 10

• Manufacturer Part Number: at42qt1481
• Description: 48-key Qmatrix Ic
• Manufacturer: ATMEL Corporation

2.7
10
Sample Resistors
AT42QT1481
Figure 2-2.
Figure 2-3.
Figure 2-4.
The sample resistors (Rs0 – Rs5) are used to perform single-slope analog-to-digital (ADC)
conversion of the acquired charge on each Cs capacitor. These resistors directly control
acquisition gain; larger values of Rs proportionately increase signal gain. Values of Rs can
range from 220 k to 1 M. 220 k is a typical value for most purposes.
Larger values for Rs also increase conversion time and may reduce the fastest possible key
sampling rate, which can impact response time especially with larger numbers of enabled keys.
Unused Y lines do not require an Rs resistor.
VCs – Nonlinear During Burst
(Burst too long, or Cs too small, or X-Y transcapacitance too large)
VCs – Poor Gain, Nonlinear During Burst
(Excess capacitance from Y line to Gnd)
VCs – Correct
X Drive
X Drive
X Drive
YnB
YnB
YnB
9621B–AT42–06/11