Electronic Circuit Characteristics; Block Diagram For Dual Ramp Analog To Digital Converter - Canon A-1 Repair Manual

4.4 Electronic Circuit Characteristics
36
(1) Light Metering .
For a light-sensing element (as in the case of the
AE-l) , an SPC which excels in l inearity and quick
response is used . The SPC' s dynamic range has been
put into practical use and the A-l is capable of
automatic exposure over a 21 EV range (EV -2
to
18).
Furthermore, stabilized performance is possible
because of provisions provide d against exposures to
environmental change. The logarithmic amplifier
(Bi-Mos construction) and di s charge circuit
(to
enable better signal response) are assimilated into
the IC, and the SPC and IC are sealed into a single
package, immune to humidity and thermal changes.
The SPC is positioned above the eyepiece as in the
case of the AS-I. The employment of a fresnel lens
to concentrate the light means mounting the A-l with
different lenses affects consistency in center-
weighted average meter reading very little.
The sensitivity distribution pattern for the A-l is slightly,
but not appreciably d iffe re nt from the pattern for
the meter reading of the AE-l.
SW2
Capacitor
Ex (Prom SPC)
c
o
SWI
Comparator
i\,
Eo
Stop
-
E ..
I -
r-''----.,
r
Timer
Counter
St.:or t
Fig. 9 Bl ock Diagram for Dual Ramp Analog to
Digital Converter