NCS36000
4
APPLICATIONS INFORMATION
Oscillator
The oscillator uses an external resistor and capacitor to set
the system clock frequency. Multiple clock frequencies can
be selected using different combinations of resistors and
capacitors. Figure 2 shows a simplifier block diagram for
the system oscillator.
+
−
+
−
OSC
13
Q
Q
SET
CLR
S
R
14
VDD
Figure 2. Block Diagram of System Oscillator Circuit
LDO Regulator
The LDO regulator provides the reference voltage for the
sensor and all other analog blocks within the system. The
nominal voltage reference for the sensor is 2.7 V
±
5%. An
external capacitor is needed on the VREF pin to guarantee
stability of the regulator.
Differential Amplifiers
The two differential amplifiers can be configured as a
bandpass filter to condition the PIR sensor signal for the post
digital signal processing. The cutoff frequencies and
passband gain are set by the external components. See
Figure 5.
10
−1
10
0
10
1
20
30
40
50
60
70
80
Figure 3. Plot Showing Typical Magnitude Response
of Differential Amplifiers When Configured as a
Bandpass Filter
Window Comparator
The window comparator compares the voltage from the
second differential amplifier to two reference voltages from
the LDO regulator. COMP_P triggers if OP2_O is greater
than the Vh voltage and COMP_N triggers if OP2_O is
lower than the Vl voltage. See Figures 4 and 5.
Vh
Vl
Vdd
Vss
Comp_P
Vdd
Vss
Comp_N
OP2_O
Vm
Figure 4. Plot Showing Functionality of Window Comparator for an Analog Input OP2_O
