(a) Interpretation: Current follower that will produce a 1.0 V output for 10.0 µA input current should be designed. Concept introduction: Operational amplifiers can be used to measure or process currents by connecting them in the current follower mode. This mode provides a nearly zero resistance load to the current source and prevents it from being loaded by a measuring device or circuit. Here, V + , V - = input voltages V s = Input difference voltage V 0 = output voltage i b = input bias current i f = feedback current i i = input current R f = feedback resistor Also, R f = V 0 i i

BuyFind

Principles of Instrumental Analysis

7th Edition
Douglas A. Skoog + 2 others
Publisher: Cengage Learning
ISBN: 9781305577213
BuyFind

Principles of Instrumental Analysis

7th Edition
Douglas A. Skoog + 2 others
Publisher: Cengage Learning
ISBN: 9781305577213

Solutions

Chapter 3, Problem 3.8QAP
Interpretation Introduction

(a)

Interpretation:

Current follower that will produce a 1.0 V output for 10.0 µA input current should be designed.

Concept introduction:

Operational amplifiers can be used to measure or process currents by connecting them in the current follower mode. This mode provides a nearly zero resistance load to the current source and prevents it from being loaded by a measuring device or circuit.

Principles of Instrumental Analysis, Chapter 3, Problem 3.8QAP , additional homework tip  1

Here,

V+, V- = input voltages

Vs = Input difference voltage

V0 = output voltage

ib = input bias current

if = feedback current

ii = input current

Rf = feedback resistor

Also,

Rf=V0ii

Interpretation Introduction

(b)

Interpretation:

Effective input resistance of the current follower designed in part (a) should be calculated.

Concept introduction:

Principles of Instrumental Analysis, Chapter 3, Problem 3.8QAP , additional homework tip  2

Here,

V+, V- = input voltages

Vs = Input difference voltage

V0 = output voltage

ib = input bias current

if = feedback current

ii = input current

Rf = feedback resistor

Ri = effective input resistance

A = open loop gain

Also,

Ri=RfA

Interpretation Introduction

(c)

Interpretation:

The percent relative error for the circuit designed in part (a) for an input current of 25 µA should be calculated.

Concept introduction:

Principles of Instrumental Analysis, Chapter 3, Problem 3.8QAP , additional homework tip  3

Here,

V+, V- = input voltages

Vs = Input difference voltage

V0 = output voltage

ib = input bias current

if = feedback current

ii = input current

Rf = feedback resistor

Ri = effective input resistance

A = open loop gain

Here,

Rf=V0ii

Also,

Ri=RfA 

Thus,

Relative error percentage = RiRL+Ri×100

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