EECS140 ANALOG CIRCUIT DESIGN LECTURES ON FEEDBACK EECS140 ANALOG CIRCUIT DESIGN LECTURES ON FEEDBACK FB 1 Feedback University of California Berkeley Basic Amplifier in Feedback Signal College of Engineering Department of Electrical Engineering and Computer Science Robert W Brodersen EECS140 Analog Circuit Design Lectures on FEEDBACK Error Signal o a ofb f Feedback Amplifier f gain of feedback amplifier a gain of basic amplifier ROBERT W BRODERSEN LECTURE 27 ROBERT W BRODERSEN EECS140 ANALOG CIRCUIT DESIGN LECTURES ON FEEDBACK EECS140 ANALOG CIRCUIT DESIGN FB 2 Feedback Cont LECTURE 27 LECTURES ON FEEDBACK FB 5 Feedback Cont in ofb There are 4 basic kinds of Feedback Circuits ofb f o i n f o Type of Feedback o a a T A o i n 1 1 a f f 1 T T Loop Gain a f a Open Loop Gain Closed loop gain Type of Sensing 1 Series Voltage Shunt Voltage 2 Shunt Current Shunt Voltage 3 Shunt Current Series Current 4 Series Voltage Series Current f Feedback Factor A a ROBERT W BRODERSEN 1 f T 1 LECTURE 27 ROBERT W BRODERSEN LECTURE 27 EECS140 ANALOG CIRCUIT DESIGN LECTURES ON FEEDBACK EECS140 ANALOG CIRCUIT DESIGN LECTURES ON FEEDBACK FB 6 Series Shunt out in ro This is a voltage amplifier a typical example is the well known configuration shown below rin a in G o R2 R1 o in f b FB 7 Series Shunt Cont fb f o o R1 f R1 R2 ROBERT W BRODERSEN LECTURE 27 EECS140 ANALOG CIRCUIT DESIGN LECTURES ON FEEDBACK Series Shunt Cont Gain Calculation EECS140 ANALOG CIRCUIT DESIGN FB 8 LECTURES ON FEEDBACK FB 9 Series Shunt Cont Ro u t fb f o in 0 t it ro it Drive output with t measure i t in fb o f o a T o 1 A in f 1 T LECTURE 27 Rout Calculation Closed Loop Output Resistance o a t a i t ro Closed Loop Gain in a o 1 a f t ro ro R out it 1 a f 1 T LECTURE 27 t a f t i n 0 f t i n 0 t a f t it ro i n 1 a f ROBERT W BRODERSEN ROBERT W BRODERSEN ROBERT W BRODERSEN A 10 f 0 1 a 50 000 T 0 1 50 000 5000 r o 100 ro R O U T 0 02 1 T LECTURE 27 EECS140 ANALOG CIRCUIT DESIGN LECTURES ON FEEDBACK Series Shunt Cont EECS140 ANALOG CIRCUIT DESIGN LECTURES ON FEEDBACK Shunt Shunt Transresistance out iin FB 10 FB 11 ro Rin Calculation i i n R in i in ii n r in aR i o in 1 T in i in r in 1 T r in Rin i fb f G o in 1 T r in iin ROBERT W BRODERSEN o ROBERT W BRODERSEN LECTURE 28 EECS140 ANALOG CIRCUIT DESIGN LECTURES ON FEEDBACK Shunt Shunt Cont LECTURE 28 EECS140 ANALOG CIRCUIT DESIGN FB 13 LECTURES ON FEEDBACK Shunt Shunt Cont Gain Calculation i f b f G o i fG fb o i i in i f b iin o a R i RS a R has units of resistance o a R i in fG o i fb 1 T o iin f G 1 T ROBERT W BRODERSEN LECTURE 28 ROBERT W BRODERSEN LECTURE 28 FB 14 EECS140 ANALOG CIRCUIT DESIGN LECTURES ON FEEDBACK EECS140 ANALOG CIRCUIT DESIGN FB 15 Shunt Shunt Cont LECTURES ON FEEDBACK Shunt Shunt Cont FB 16 Rout Calculation Closed Loop Output Resistance Rin Calculation R IN t R O U T it i in o t i i i n fG o iin a R f G i i in 0 i t i fb i in i 1 aR f R IN i in 0 i i fb f G o ri n i in 1 T o it r o a R i i t r o a R f G o ro o RO U T it 1 T ROBERT W BRODERSEN ROBERT W BRODERSEN LECTURE 28 EECS140 ANALOG CIRCUIT DESIGN LECTURES ON FEEDBACK io i iin LECTURES ON FEEDBACK Shunt Series Cont T a i fi i fb fi io Gain Calculation ai i ri n EECS140 ANALOG CIRCUIT DESIGN FB 17 Shunt Series Current Amp i out iin LECTURE 28 ro i T o 1 iin f i 1 T Rin Calculation i f b f i o io r in R I N 1 T Rout Calculation Closed Loop Output Resistance R OUT r o 1 T ROBERT W BRODERSEN LECTURE 28 ROBERT W BRODERSEN LECTURE 28 FB 18 EECS140 ANALOG CIRCUIT DESIGN LECTURES ON FEEDBACK ro in FB 20 Gain Calculation a G Series Series Cont T a G fR fb fR io io LECTURES ON FEEDBACK FB 19 Series Series Transconductance i out in r in EECS140 ANALOG CIRCUIT DESIGN io T 1 A G in fR 1 T Rin Calculation R I N r in 1 T io i f b f R o Rout Calculation Closed Loop Output Resistance R O U T ro 1 T ROBERT W BRODERSEN LECTURE 28 ROBERT W BRODERSEN EECS140 ANALOG CIRCUIT DESIGN LECTURES ON FEEDBACK a 10 i n o R 2 9k fb FB 22 R1 T a f a R 1 R 2 r in ro R1 ri n a fb o R1 R2 No loading means we don t taken into account the drop across r o due to R 1 R 2 ROBERT W BRODERSEN Series Shunt Example Cont 5 1k T 10 10 4 1k 9k r o 10 k R2 LECTURES ON FEEDBACK o T 1 A i n f 1 T 5 R 1 1k EECS140 ANALOG CIRCUIT DESIGN FB 21 Series Shunt Example Without Loading LECTURE 28 1 10 4 A 10 000 0 1 1 104 precisely 10 to 4 decimal places f fb o R i n r in 1 T 1 10 4 fb R1 f 0 1 o R1 R 2 ro 10 4 R O U T 4 1 1 T 1 10 LECTURE 28 ROBERT W BRODERSEN LECTURE 28 EECS140 ANALOG CIRCUIT DESIGN LECTURES ON FEEDBACK R IN R2 R1 i ro in i in R1 R1 R2 R1 R IN i fb R2 i o o o R1 a R 1 aR in iin i n R1 FB 25 Shunt Shunt Example Cont o o LECTURES ON FEEDBACK FB 24 Shunt Shunt Example Without Loading EECS140 ANALOG CIRCUIT DESIGN iin in R1 i i i i n i fb R2 ROBERT W BRODERSEN LECTURE 28 EECS140 ANALOG CIRCUIT DESIGN LECTURES ON FEEDBACK Shunt Shunt Example Cont ro FB 26 LECTURES ON FEEDBACK Shunt Shunt Example Cont 1 R 5 1 4 T a R a 1 10 1 1 10 R 2 9 R 2 i R1 EECS140 ANALOG CIRCUIT DESIGN 4 o 1 T 1 1 10 A R R 2 4 R 2 9k i in f 1 T 1 1 1 10 a a R 1 i i R 1 But we want O in i n i in R1 i fb O …
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