Department of Electronics & Telecommunication Engineering

A n a l o g S y s t e m A n d D e s i g n

Dual Input Balance Output Differential Amplifier

Submitted By-Ashish Pandey (30)

Y e a r - 2 n d | S e m e s t e r – 4 t h | S e c t i o n - C

(Session 2014-2015)

Guided By-Ms. Swati Dixit,

Assistant Professor,Department of ET&C,

Dual Input Balanced Output Differential Amplifier uses two input signals, the configuration is said to be dual input and the output voltage is measured between two collectors, it is referred to as a balanced output because both the collectors are at the same dc potential w.r.t. ground.

Introduction:-

Description:- The circuit is shown in fig.1., V1 and V2 are the two inputs, applied to the bases of Q1 and Q2

transistors. The output voltage is measured between the two collectors C1 and C2 , which are at same dc potentials.

Working:-

The collector C1 and C2 are connected to the +ve supply voltage +vcc to through a resistance Rc.

The magnitude of the supply voltages +vcc and –vee must be equal. All the componet of the two emitter biased Circuit must be match for proper operation.

Two dual input vi1 and vi2 from the collectors c1 and c2 of the match transistor T1 and T2 the source resistance Rs and base spreading resistance rbb are assumed to be Zero.

The circuit diagram of Dual Input Balance output Differential Amplifier using BJT is Shown in figure It consist of two matched transistor T1 and T2, whose emitters are joins togather and biased by Constant current source.

DC Circuit Analysis:-

To obtain the operating point (ICC and VCEQ) for differential amplifier dc equivalent circuit is drawn by reducing the input voltages v1 and v2 to zero.

The internal resistances of the input signals are denoted by RS because RS1= RS2. Since both emitter biased sections of the different amplifier are symmetrical in all respects, therefore, the operating point for only one section need to be determined.

The same values of ICQ and VCEQ can be used for second transistor Q2.

AC Circuit Analysis:-

To find the voltage gain Ad and the input resistance Ri of the differential amplifier, the ac equivalent circuit is drawn using r-parameters. The dc voltages are reduced to zero and the ac equivalent of CE configuration is used.

Since the two dc emitter currents are equal. Therefore, resistance re’1 and re’2 are also equal and designated by re’.

This voltage across each collector resistance is shown 180° out of phase with respect to the input voltages v1 and v2.

This is same as in CE configuration. The collector C2 is assumed to be more positive with respect to collector C1 even though both are negative with respect to to ground.

Differential Gain

Advantages:-

It can be connected directly to obtained high gain.

It can also remove lower cut-off frequency due to coupling capacitor.

Application:-

Use as a subtractor circuit.

THANK YOU