HT761X
·
Options for setting the comparator window to be
1
,
16
1
1
or (V
DD
-V
EE
).
11.3
9
1
(V
DD
-V
EE
).
The default is
16
PIR Amplifier
Consult the diagram below for details on the PIR front
end amplifier.
In the Fig.2 below there are 2 op-amps with different ap-
plications. OP1 can be used independently as a first
stage inverting or non-inverting amplifier for the PIR.
V
O P 1 O
O P 1 N
O P 1 P
V
O P 2 O
O P 2 N
O P 2 P
O P 2
C P
D D
If the window level fails to be specified the default win-
1
(V
DD
-V
EE
). The preset voltage of
dow is set to
16
V
DD
-V
EE
is 4V. The default values of V
CP
and V
CN
are
4
therefore 0.25V, (
V ).
16
Second Stage Amplifier
Usually the second stage PIR amplifier is a simple ca-
pacitively coupled inverting amplifier with a low pass
configuration. The noninverting input terminal is biased
to the center point of the comparator window and the
output of the second stage amplifier is directly coupled
to the comparator center point.
In Fig.3 OP2P is directly connected to the comparator
window center, and with the C3 filter it can act as the
R2
, low cutoff
bias for OP2. For this configuration A
V
=
R1
1
frequency f
L
=
, high cutoff frequency
2
p
R1C1
1
f
H
=
. By changing the value of R2 the sensitiv-
2
p
R2C2
ity can be varied. C1 and C3 should be of low leakage
types to prevent the DC operating point from changing
due to current leakage.
Each op-amp current consumption is approximately
5mA with the op-amps and comparator¢s working volt-
age all provided by the regulator.
Consult the following diagrams for typical PIR front end
circuit.
First Stage of PIR Amplifier
Fig.4 shows a typical first stage amplifier. C2 and R2
form a simple low pass filter with cut off frequency at
7Hz. The low frequency response is governed by R1
and C1 with cut-off frequency at 0.33Hz.
A
V
=
( R1+ R2 )
R
1
O P 1
C o m p a ra to r
V
C N
V E E
R e g u la to r
Fig.2 PIR Amplifier
As the output of OP2 is directly connected to the input of
the comparator, it is used as a second stage amplifying
device. The non-inverting input of OP2 is connected to
the comparator¢s window center point and can be used
to check this voltage and to provide a bias voltage that is
equal to the center point voltage of the comparator. In
Fig.2 the comparator can have 3 window levels set by
1
1
(V
DD
-V
EE
), 2.
(V
DD
-V
EE
),
mask option. 1.
16
11.3
1
3. (V
DD
-V
EE
).
9
V
O P 2 O
R 1
2 2 k
W
C 2
0 .0 2 2
m
F
D D
R
W
R 2
1 M
W
O P 2 N
O P 2 P
O P 2
R
W
fir s t s ta g e
o u tp u t
C 1
2 2
m
F
V
D D
R
W
R
W
V E E
C 3
1 0
m
F
Fig.3 Typical Second Stage Amplifier
Rev. 1.30
6
October 12, 2009
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
