SLIDE 1
Spring 2014 Comparators 2
Outline
- Comparator limitations
- Latched comparators
Comparators Dag T. Wisland Spring 2014 Outline Comparator - - PowerPoint PPT Presentation
Comparators Dag T. Wisland Spring 2014 Outline Comparator - - PowerPoint PPT Presentation
INF4420 Comparators Dag T. Wisland Spring 2014 Outline Comparator limitations Latched comparators Spring 2014 Comparators 2 Introduction Spring 2014 Comparators 3 Comparator performance Spring 2014 Comparators 4 The opamp as a
SLIDE 2
SLIDE 3
Introduction
Spring 2014 Comparators 3
SLIDE 4
Comparator performance
Spring 2014 Comparators 4
SLIDE 5
The opamp as a comparator
We already know how to make an opamp. Can we use it as a comparator? The offset voltage is typically large, but we cancel the offset by sampling:
Spring 2014 Comparators 5
SLIDE 6
The opamp as a comparator
Spring 2014 Comparators 6
SLIDE 7
The opamp as a comparator
Spring 2014 Comparators 7
SLIDE 8
The opamp as a comparator
Spring 2014 Comparators 8
SLIDE 9
Charge injection and clock feedthrough
Spring 2014 Comparators 9
SLIDE 10
Latched comparators
- Low gain preamplifier and latch example
Spring 2014 Comparators 10
SLIDE 11
Latched comparators
Spring 2014 Comparators 11
SLIDE 12
Latched comparators
- If the voltage difference is too small,
metastability occurs. The latch is not able to correctly resolve the input.
- Two halves of the latch are subject to mismatch
(systematic and random)
- Possible to tune the offset. Program some
voltage to compensate for the offset. However, we need to find an appropriate voltage to cancel the offset.
Spring 2014 Comparators 12
SLIDE 13
Latched comparator example
Van Elzakker, ISSCC, 2008
Spring 2014 Comparators 13