SUMMING AND DIFFERENCE AMPLIFIER

Summing Amplifier The summing amplifier is a versatile device for

combining signals. It can either add signals directly, or scale them to fit some predetermined combination rule.

Summing several signals with equal gains is done in an audio mixer.

A summing amplifier with different resistors on the inputs gives a weighted sum. This can be used to convert a binary number to a voltage in a digital to analog converter.

A summing amplifier can be used to apply a DC offset voltage along with an AC signal voltage. This is done in a LED modulation circuit to keep the LED in its linear operating range.

The Summing Amplifier

Scale factors for the 2 inputs can be independently adjusted by the proper choice of R2 and R1.

Any number of inputs can be connected to a summing junction through extra resistors.

This circuit can be used as a simple digital-to-analog converter. This will be illustrated in more detail, later.

11v

1i R22v

2i R3ov

3i R

Since the negative amplifier input is at virtual ground,

Since i-=0, i3= i1 + i2,

voR

3R1

v1R

3R

2v2

Difference Amplifier Then  differential amplifiers amplify the

difference between two voltages making this type of operational amplifier circuit a Subtractor unlike a summing amplifier which adds or sums together the input voltages. This type of operational amplifier circuit is commonly known as a Differential Amplifier configuration and is show in the next slide.

The Difference Amplifier

This circuit is also called a differential amplifier, since it amplifies the difference between the input signals.

Rin2 is series combination of R1 and R2 because i+ is zero.

For v2=0, Rin1= R1, as the circuit reduces to an inverting amplifier.

For general case, i1 is a function of both v1 and v2.

1v1

2-v1

21)-v1v(1

2-v

21i-v22i-vov

R

R

R

RR

R

R

RR

vR

2R1R

2v2

Also,

Since v-= v+ )2v1(v1

2v R

Ro

For R2= R1)2v1(vv o

Difference Amplifier: Example Problem: Determine vo

Given Data: R1= 10kW, R2 =100kW, v1=5 V, v2=3 V Assumptions: Ideal op amp. Hence, v-= v+ and i-= i+=

0. Analysis: Using dc values,

AdmR

2R1

100kW10kW

10

VoAdm V1 V

2

10(5 3)

Vo 20.0 V

Here Adm is called the “differential mode voltage gain” of the difference amplifier.

THANK YOU FOR WATCHING