week_11

# week_11 - 98 Operational Amplifier Need for high gain...

This preview shows pages 1–5. Sign up to view the full content.

98 Operational Amplifier Need for high gain stage: in V . A out V DD V = A AV V in out problem is that with having even small DC component will be saturated to either or ground. in V out V DD V Assume ) 2 ( . 1 . 0 100 ) 2 ( . 1 1 000 , 100 3 ft Cos v v AV V ft Cos v mvDC V A v V in out in DD π µ + = = + = = = We don’t have 100v bias on the amplifier = v V V DD out 3 so the gain stage will not work if DC signal is present. How about noise? noise v ft Cos v V noise v ft Cos v V out in 1 ) 2 ( . 1 . 0 10 ) 2 ( . 1 + = + = Signal

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
99 Therefore the noise masks the output performance because it is amplified with the same gain as signal being amplified. Solution Æ use high gain differential amplifier. If your input signal has DC component or common mode noise component it will not be amplified by the differential amplifier. in V . A out V DD + V ~ + ~ DC V 2 noise V Assume: ) ( . 1 100 ) 2 ( 1 01 . 0 000 , 100 mod mod mod mod noise DC e common diff in e diff out DC noise diff in e common e diff V V A V A V v V ac v V ft vCos V A A + + = = = = = = µ π amp diff the of noise added v v ft vCos noise + + + = 1 01 . 0 ) 2 ( 1 . 0
100 High gain differential-stage are called OPAMPS . output DD V + ) ( input v e + . ) ( input v e Usually they are built as following: V DD is used to stabilize the system when if is need with feedback. cmp C Example of such OPAMP in V 1 A out V + 2 A 1 cmp C Diff-input stage High gain stage Buffer for driving high output current 6 . 1 300 2 Q cmp C in v b R . DD V . . 6 . 1 100 6 . 1 25 6 . 1 25 6 . 1 25 6 . 1 25 6 . 1 25 DD V . . DD V out + in v v .. 6 . 1 300 6 . 1 300 . . . DD V . 1 Q 4 Q 3 Q 6 Q 5 Q 8 Q 7 Q 9 Q 6 . 1 300 6 . 1 300 6 . 1 150 6 . 1 150 6 . 1 500 6 . 1 500 Biasing Diff-amplifier Gain stage buffer

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
101 Let’s simplify it: Biasing : 2 PMOS current mirror 4 NMOS Æ cascode current source with source degeneration = K R b 8 . DD V . 15 Q 13 Q 13 I 15 I 10 I 11 I 2 13 2 15 13 15 2 15 15 15 15 2 13 13 13 13 15 11 10 ) ( ) ( ) ( 2 ) ( 2 13 15 15 15 13 13 n n n n t GS t GS t GS ox n b GS GS t GS ox n V V W V V W I I V V L W C I R I V V V V L W C I I I I I = = × = × + = × = = = = µ 2 15 15 15 2 15 15 15 15 15 13 15 ) ( 2 ) ( 2 2 2 ) ( ) ( 2 25 100 15 15 15 15 13 15 13 15 b ox n t GS ox n b t GS t b GS GS t GS GS t GS t GS R I L W C V V L W C I R I V V V R I V V V V V V V V V m W m W n n n n n n × = × = = = = = = = m W m L v A C K
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 15

week_11 - 98 Operational Amplifier Need for high gain...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online