NCS36000

www.onsemi.com

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