Pulnix TM-6CN, Руководство по эксплуатации

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SECTION 7
CCD CHARACTERISTICS AND
OPERATION
7.1 THEORY OF OPERATION (Operation principle of
the CCD)
A CCD (Charge Coupled Device) consists of MOS
(Metal-Oxide-Semiconductor) capacitors arranged in a
regular array. It basically performs three functions con-
nected with handling charges:
1. Photoelectric conversion (photosensor).
Incident light generates charges on the MOS capaci-
tors, with the quantity of charge being proportional to
the brightness.
2. Accumulation of charges.
When a voltage is applied to the electrodes of the MOS
capacitors, an electric potential well is formed in the sil-
icon layer. The charge is accumulated in this well.
3. Transmission of charge
When a high voltage is applied to the electrodes, a
deeper well is formed; when a low voltage is applied, a
shallower well is formed. In the CCD, this property is
used to transmit the charge. When a high voltage is
applied to the electrodes, a deep electric potential well
is formed, and charge flows in from a neighboring well.
When this is repeated over and over among the regu-
larly arranged electrodes, the charge is transferred
from one MOS capacitor to another. This is the princi-
ple of CCD charge transmission.
7.2 MECHANISM OF CCD CHARGE TRANSFER
1. Vertical transfer
The vertical shift register transfers charges using a four-
phase drive mode. Figure 1 shows an example of the
changes which can occur in potential wells in successive
time intervals. At t0, the electrode voltages are (V1 =
V2)>(V3 = V4), so the potential wells are deeper toward
the electrode at the higher voltages V1 and V2.
Charges accumulate in these deep wells. At t1, the
electrode voltages are (V1 = V2 = V3)>(V4), so the
charges accumulate in the wells toward the electrode at
V1, V2 and V3. At t2, the electrode voltages are (V2 =
V3)>(V4 = V1), so the charges accumulate in the wells
toward the electrode at V2 and V3. Electrode voltage
states at t3 and after are shown below.
t3(V2 = V3 = V4)>(V1)
t4(V3 = V4)>(V1 = V2)
t5(V4>(V1 = V2 = V3)
t6(V4 = V1)>(V2 = V3)
t7(V4 = V1 = V2)>(V3)
t8(V1 = V2)>(V3 = V4) (Initial state)
These operations are repeated to execute the vertical
transfer.
2. Horizontal transfer
The horizontal shift register transfers charges using a
two-phase drive mode. Figure 2 shows an example of
the changes which can occur in the potential wells in
successive time intervals. At t1, the electrode voltages
are H1>H2, so the potential wells are deeper toward
the electrode of the higher voltage H1. The charges
accumulate in these wells. At t2, the electrode volt-
ages H1 and H2 are inverted, the wells toward the
electrode at voltage H2 become deeper while the wells
toward the electrode at voltage H1 become shallower.
So the wells at H2 are deeper than those at H1, the
t0
V1
V2
V3
transfer direction
time
V1
V2
V3
V4
V4
t0
t1
t2
t3
t4
t5
t6
t7
t8
t1 t2
t3 t4 t5
t6
t7 t8
t1
t2
t3
time
potential profile
transfer direction
Operating Pulse Waveforms (ø1, ø2 or øH1, øH2)
(minus) shows lower
impurity concentration
potential profile
P - sub
ø2
ø1
t
N- N N- N N- N N- N N-
N, N- * : N type impurity
* -
V1
V0
ø2
V1
V0
ø1
V1 > VO
t1 t2 t3