
Sensors in Engineering and Science 43
0 50 100 150 200 250 300 350 400 450 500
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Time, µs
Amplitude, V
FIGURE 2.7
Charge detector output upon capture of a charged (∼1 pC) ethanol micro-
droplet [10]. Note the sensor’s short time response, which was less than ∼100
µs.
The charge amplifier is an operational amplifier whose positive and nega-
tive inputs are the outputs of the two electrodes. A resistor is placed between
one electrode and the positive input. A parallel resistor, R
f
, and capacitor,
C
f
, are connected as a feedback loop between the amplifier’s output and its
negative input. In this manner, the current output of the sensor, whic ...