Op amps find extensive use in a wide variety of circuits, and their appropriate specification for a particular application requires knowledge of relevant data-sheet parameters. Data sheet specifications are divided into two general categories: dc parameters and ac parameters. The dc parameters represent internal errors that occur as a result of mismatches between devices and
components inside the op amp. These errors are always present from the time the power is turned on (i.e., before, during and after any input signal is applied), and they determine how precisely the output matches the ideal op-amp model. Thus the precision of the op amp is determined by the magnitude of the dc errors.
1 In t ro d u c t io n ..................................................................................................................... 3
2 In p u t O f fs e t V o l tag e D e f in e d ..................................................................................... 4
3 Cause of VI O ..................................................................................................................... 5
4 V I O a n d T e m p e r a tu r e D r i f t in th e M a jo r D e v ic e T y p e s ...................................... 5
4 . 1 B i p o l a r........................................................................................................................ 6
4 . 2 B i F E T ......................................................................................................................... 8
4 . 3 C M O S ........................................................................................................................ 9
5 M a n ufa cturer Me as u rem e nt, Trim, an d S p e cific a tio n of VIO ........................... 9
5 . 1 M e a s u r e m e n t........................................................................................................... 9
5 . 2 T r im...........................................................................................................................1 0
5 . 3 S p e c i f i c a t io n s ........................................................................................................1 0
6 Impact of VI O on Circ uit D e sign an d M e th o d s o f Cor r e c tion ........................ 1 4
6 . 1 A C C o u p l i n g ...........................................................................................................1 5
6.2 D C F e e d b a c k.........................................................................................................1 7
6 . 3 I n t e r n a l C a l ib r a t io n ...............................................................................................1 8
6 . 4 E x t e r n a l C a l ib r a t io n .............................................................................................1 9
7 S u m m a r y ........................................................................................................................ 2 1
R e f e r e n c e s........................................................................................................................... 2 2
Figures
1 I d e a l O p - A m p M o d e l a n d M o d e l P a r am e t e r s ....................................................... 3
2 N o n i d e a l O p - A m p M o d e l ............................................................................................ 4
3 D is t r ib u tio n o f V I O fo r th e T L V 2 7 2 1 .......................................................................... 4
4 S i m p l if ie d D i f f e re nt i a l-P a i r A m p l if ie r . Q 1 a nd Q 2 A r e B J T, F E T o r M O S . ... 5
5 B ip o la r T ra n s is to r D i f fe re n t ial-P a i r C irc u i t . (a) B a s ic C ircu i t a n d (b)
G e n e r a l C i r c u it U se d to C a lc u l a t e VI O..................................................................... 6
6 S im p l i f ie d S e r v o - L o o p T e s t C i r c u i t ........................................................................ 1 0
7 G r a p h o f V I O D r if t O v e r 0 –7 0°C .......................................................................... 1 3 1 2
8 V I O v s V I C f o r ( a ) T L C 0 7 1 a n d (b ) T L C 0 8 1 O p A m p s .................................. 1 4 1 3
SLOA059
2 DC Parameters: Input Offset Voltage (VIO)
9 V I O C h a n g e s W ith C o m m o n M o d e In pu t V o lta g e (VIC) f o r (a) the T L V 2 4 7 x
a n d ( b ) t h e T L V 2 7 3 1 ...................................................................................................1 4
1 0 In v e r t in g O p - A m p C i r c u it W i th VI O I n c lu d e d ........................................................1 5
1 1 A C C o u p l e d I n v e r ti n g A m p l i f ie r ...............................................................................1 6
1 2 G e n e ra l F o rm o f DC F e e d b a c k L o o p ....................................................................1 7
1 3 S im p l ifie d B lo c k D ia g r a m o f th e T L C 26 5 4 Ch o p p e r -St a b il iz e d A m p l if ie r ..1 8
1 4 B l o c k D i a g r a m o f C h a n n e l O n e o f t h e T L C 4 5 0 2 ...............................................1 9
1 5 T y p i c a l N u l l C o n f ig u r a t i o n o f a n A m p l if i e r............................................................2 0
1 6 VIO A d ju s tm e n t W ith a P o te n tio m e te r a n d L o w T e m p e ra tu r e C o e ff icie n t
R e s i s t o r...........................................................................................................................2 0
Tables
1 R a n g e o f I n p u t O f fs e t V o l t a g e a n d D r if t P e r D e v i c e P r o c e s s .......................... 6
2 Example of VI O S pe c if ic a t io n s T a k e n F r o m T L E 2 0 2 1 D a ta S h e e t
( S L O S 1 9 1 ) .....................................................................................................................1 1
3 C o n v e r t e r R e s o l u t io n ..................................................................................................1 7