tailieunhanh - Introduction to Electronics - Part 3

Op Amp Circuits - The Inverting Amplifier Điện áp tăng Bởi vì các op amp lý tưởng đã Ri = ∞, hiện tại vào các yếu tố đầu vào sẽ là số không. Điều này có nghĩa i1 = i2, ví dụ, điện trở R1 và R2 hình thức một dividerIII điện áp Vì vậy, chúng ta có thể sử dụng chồng chất để tìm thấy điện áp v-. (Hãy nhớ rằng việc thực hiện nhanh chóng trên trang | Op Amp Circuits - The Inverting Amplifier Introduction to Electronics 31 Op Amp Circuits - The Inverting Amplifier Let s put our ideal op amp concepts to work in this basic circuit Voltage Gain Because the ideal op amp has Rị the current into the inputs will be zero. This means i1 i2 . resistors R1 and R2 form a voltage dividerlll Therefore we can use superposition to find the voltage v_ . Remember the quick exercise on p. 4 This is the identical problem viR vR1 - R1 R2 Now because there is negative feedback vo takes on whatever value that causes v - v 0 and v 0 Thus setting eq. 35 to zero we can solve for vo vR voRi 0 vo - R2 v Av -R 36 I 1 R 1 Op Amp Circuits - The Inverting Amplifier Introduction to Electronics 32 Fig. 45. Inverting amplifier circuit Fig. 44 repeated . Input Resistance This means resistance seen by the signal source v not the input resistance of the op amp which is infinite. Because v_ 0 the voltage across R1 is v . Thus ii - R Rin 11 v R vi 1 Ri 37 Output Resistance This is the Thevenin resistance which would be seen by a load looking back into the circuit Fig. 45 does not show a load attached . Our op amp is ideal its Thevenin output resistance is zero Ro 0 38 Op Amp Circuits - The Noninverting Amplifier Introduction to Electronics 33 Op Amp Circuits - The Noninverting Amplifier If we switch the v and ground connections on the inverting amplifier we obtain the noninverting amplifier. Voltage Gain This time our rules of operation and a voltage divider equation lead to. vi V v- r r vo 39 from which. R. R2. L . R2 Y . . R2 vo p v 1 p vi Av 1 2 40 R1 V R1J R1 Input and Output Resistance The source is connected directly to the ideal op amp so Rin Ri tt 41 A load sees the same ideal Thevenin resistance as in the inverting case Ro 0 42