NMOS linear image sensor
s
Driver circuit
S3901/S3904 series do not require any DC voltage supply
for operation. However, the Vss, Vsub and all NC terminals
must be grounded. A start pulse
φst
and 2-phase clock pulses
φ1, φ2
are needed to drive the shift register. These start and
clock pulses are positive going pulses and CMOS logic com-
patible.
The 2-phase clock pulses
φ1, φ2
can be either completely
separated or complementary. However, both pulses must not
be “High” at the same time.
A clock pulse space (X1 and X2 in Figure 7) of a “rise time/fall
time - 20” ns or more should be input if the rise and fall times
of
φ1, φ2
are longer than 20 ns. The
φ1
and
φ2
clock pulses
must be held at “High” at least 200 ns. Since the photodiode
signal is obtained at the rise of each
φ2
pulse, the clock pulse
frequency will equal the video data rate.
S3901/S3904 series
The amplitude of start pulse
φst
is the same as the
φ1
and
φ2
pulses. The shift register starts the scanning at the “High”
level of
φst,
so the start pulse interval determines the length of
signal accumulation time. The
φst
pulse must be held “High”
at least 200 ns and overlap with
φ2
at least for 200 ns. To
operate the shift register correctly,
φ2
must change from the
“High” level to the “Low” level only once during “High” level of
φst.
The timing chart for each pulse is shown in Figure 7.
s
End of scan
The end of scan (EOS) signal appears in synchronization
with the
φ2
timing right after the last photodiode is addressed,
and the EOS terminal should be pulled up at 5 V using a 10
kΩ resistor.
Figure 7 Timing chart for driver circuit
st
1
2
V s (H)
V s (L)
V
V
V
V
1 (H)
1 (L)
2 (H)
2 (L)
tpw s
tpw 1
Figure 8 Video bias voltage margin
10
tvd
ACTIVE VIDEO OUTPUT
VIDEO BIAS VOLTAGE (V)
tpw 2
8
6
END OF SCAN
OM
EC
R
4
E
ND
ME
D
S
BIA
MA
X.
tr s
st
tf s
VIDEO BIAS RANGE
2
MIN.
0
4
5
6
7
8
9
10
tr 1
tf 1
1
X1
2
t ov
tr 2
X2
tf 2
CLOCK PULSE AMPLITUDE (V)
s
Signal readout circuit
There are two methods for reading out the signal from an NMOS
linear image sensor. One is a current detection method using
the load resistance and the other is a current integration method
using a charge amplifier. In either readout method, a positive
bias must be applied to the video line because photodiode
anodes of NMOS linear image sensors are set at 0 V (Vss).
Figure 8 shows a typical video bias voltage margin. As the clock
pulse amplitude is higher, the video bias voltage can be set
larger so the saturation charge can be increased. The rise and
fall times of the video output waveform can be shortened if the
video bias voltage is reduced while the clock pulse amplitude is
still higher. When the amplitude of
φ1, φ2
and
φst
is 5 V, setting
the video bias voltage at 2 V is recommended.
To obtain good linearity, using the current integration method is
advised. In this method, the integration capacitance is reset to
the reference voltage level immediately before each photodiode
is addressed and the signal charge is then stored as an integra-
tion capacitive charge when the address switch turns on. Fig-
ures 9 and 10 show a typical current integration circuit and its
pulse timing chart. To ensure stable output, the rise of a reset
pulse must be delayed at least 50 ns from the fall of
φ2.
KMPDC0022EA
KMPDB0043EA
Hamamatsu provides the following driver circuits and related
products (sold separately).
Product
name
Type No.
C7883
C7883G
Driver
circuit
C7884
C7884G
C7884-01
C7884G-01
Pulse
C8225-01
generator
Cable
A8226
Content
High-speed
driver circuit
C7883
+ C8225-01
Precision
driver circuit
C7884
+ C8225-01
High precision
driver circuit
C7884-01
+ C8225-01
C7883,
C7884 series
C7883 to
C7885 series
Feature
High-speed operation
Single power supply
(+15 V) operation
Compact
Low noise
Good output linearity
Boxcar waveform output
Ultra-low noise
Good output linearity
Boxcar waveform output
BNC, length 1 m
HAMAMATSU [ HAMAMATSU CORPORATION ]
