Method and apparatus for converting a low dynamic range analog signal to a large dynamic range floating-point digital representation
First Claim
1. A method for converting an analog signal to a cumulative digital representation using an analog-to-digital converter with an input dynamic range, the cumulative digital representation can have a dynamic range greater than the input dynamic range, the method comprising:
- (a) receiving the analog signal from an photodetector after the photodetector is exposed to a scene for a total exposure time T, the analog signal is monotonically changing with respect to T;
(b) sampling the analog signal at subsequent times t=T1>
0,t=T2>
T1,t=T3>
T2, . . . t=TM>
TM−
1 to produce respective digital representations of the analog signal, wherein TM<
=T; and
(c) combining the respective digital representations into the cumulative digital representation.
0 Assignments
0 Petitions
Accused Products
Abstract
An analog-to-digital conversion scheme allows the conversion of a small dynamic range analog signal into a floating-point, digital representation with a larger dynamic range. A montonically changing analog signal is reset to a reference value at time t=0. The analog signal is then sub-converted by an analog-to-digital converter with maximum input signal level Ss to corresponding digital representations at several sub-conversion times t=T2>T1, t=T3>T2, . . . t=TM>TM−1, where TM≦T. These digital representations are then suitably combined to produce a cumulative, floating-point digital representation which accurately represents the analog signal even if the analog signal has a value greater than Ss at time t=T.
183 Citations
17 Claims
-
1. A method for converting an analog signal to a cumulative digital representation using an analog-to-digital converter with an input dynamic range, the cumulative digital representation can have a dynamic range greater than the input dynamic range, the method comprising:
-
(a) receiving the analog signal from an photodetector after the photodetector is exposed to a scene for a total exposure time T, the analog signal is monotonically changing with respect to T;
(b) sampling the analog signal at subsequent times t=T1>
0,t=T2>
T1,t=T3>
T2, . . . t=TM>
TM−
1 to produce respective digital representations of the analog signal, wherein TM<
=T; and
(c) combining the respective digital representations into the cumulative digital representation. - View Dependent Claims (2, 3, 4, 5)
(a) appending the Nth (rightmost) bit of the digital representation corresponding to T2 to the right of the digital representation corresponding to T1 to form an N+1 bit intermediate digital representation;
(b) appending the Nth (rightmost) bit of the digital representation corresponding to T3 to the right of the intermediate digital representation to form a new intermediate digital representation; and
(c) repeating b) for the Nth (rightmost) bit of the digital representations corresponding to T4, T5, . . . TM until only an N+M−
1 bit intermediate digital representation remains, the N+M−
1 bit intermediate digital representation being the cumulative, floating-point, digital representation.
-
-
6. An analog-to-digital conversion circuit for converting an analog signal to a cumulative digital representation having a dynamic range greater than an input dynamic range of the analog-to-digital conversion circuit, the circuit comprising:
-
(a) a first signal generator for generating a first signal having a plurality of levels;
(b) a comparator having a first input connected to receive the first signal and a second input connected to receive the analog signal;
(c) a binary signal generator for generating a series of binary signals; and
(d) a latch having a first input coupled to receive an output of the comparator, the latch also having a data input coupled to receive the binary signals, the output of the comparator controlling when the latch provides an output signal corresponding to the binary signals applied to the data input, wherein the analog signal is received from a photodetector after the photodetector is exposed to a scene for a total exposure time T;
wherein the latch provides a first N-bit digital code representing the analog signal at a first sampling time T1>
0, andwherein the latch provides at least a portion of subsequent N-bit digital codes representing the analog signal_sampled at subsequent sampling times T2>
T1, T3>
T2, . . . TM<
TM−
1, and TM<
=T.- View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
-
Specification