OBJECTIVES: 1.To obtain the frequency response of the Two Stage RC Coupled Amplifier
2. To find the Voltage Gain and Bandwidth.
TINA PRO SOFTWARE
This is most popular type of coupling as it provides excellent audio fidelity. A coupling capacitor is used to connect output of first stage to input of second stage. Resistances R5, R2, R3 form biasing and stabilization network for Q1 and R7, R8 and R9 for Q2. Emitter bypass capacitor offers low reactance paths to signal. coupling Capacitor transmits AC signal, blocks DC. Cascaded stages amplify the signal, the overall gain is increased. Thus coupling is done for more gain and overall gain of two stages equals to A=A1*A2
A1=voltage gain of first stage=V01/Vi
A2=voltage gain of second stage= V02/V01
When ac signal is applied to the base of the transistor, its amplified output appears across the collector resistor Rc. It is given to the second stage for further amplification and signal appears with more strength. Frequency response curve is obtained by plotting a graph between frequency and gain in dB .The gain is constant in mid frequency range and gain decreases on both sides of the mid frequency range. The gain decreases in the low frequency range due to coupling capacitor Cc and at high frequencies due to junction capacitance Cbe.
Start TINA software. A blank circuit window will appear on the screen along with a component tool bar.
Using component tool bar, place all the components on the circuit window and wire the circuit.
Connect the circuit as shown in circuit diagram
Apply the input of 10mV peak-to-peak and 1 KHz frequency sinusoidal, using AC Voltage Source.
From drop down menu select Transient analysis in the analysis option.
Input and output waveforms will be displayed. Measure the Output Voltage Vo (p-p) both at the first stage and second stage.
To find frequency response select AC analysis from drop down menu. Calculate the bandwidth and gain in the response displayed.
INPUT WAVE FORM:
FIRST STAGE OUTPUT:
SECOND STAGE OUTPUT:
All connections are to be connected properly.
Transistor terminals must be identified properly.
RESULT: Thus voltage gain and bandwidth of two stage RC coupled amplifier is calculated and its frequency response is observed.
Students are able to
Design and analyze Two stage RC-Coupled amplifier.
1.What is the necessity of cascading?
Ans: Cascading will increase the signal strength.
2..What is 3dB bandwidth?
Ans: Bandwidth is the difference between the upper and lower frequencies in a continuous set of frequencies. It is typically measured in hertz, and may sometimes refer to passband bandwidth, sometimes to baseband bandwidth, depending on context. Passband bandwidth is the difference between the upper and lower cutoff frequencies of, for example, a bandpass filter, a communication channel, or a signal spectrum. In case of a low-pass filter or baseband signal, the bandwidth is equal to its upper cutoff frequency.
3.Why RC coupling is preferred in audio range?
Ans: The RC coupling provides a constant amplification over a wide range of frequencies.
4.Which type of coupling is preferred and why?
Ans: RC coupling used in operational amplifiers , power supplies
5.Explain various types of Capacitors?
Ans:1.Input coupling capacitor used to couple the AC to input signal to amplifier blocks DC signal, 2.Emitter by-pass capacitor used to reduce the signal drop to ground and 3.Output coupling capacitor used to couple the AC output of amplifier to next stage without attenuation.
6.What is loading effect?
Ans: It tells how well power supply maintenance the output voltage for change in load resistance.
7.Why it is known as RC coupling?
Ans: In amplifier circuit the coupling to the next stage using resistor and capacitor (RC) combination can be called as a RC coupling.
8.What is the purpose of emitter bypass capacitor?
Ans: In amplifier circuit RE is feedback resistor will decrease the voltage gain for the fluctuations in current IE ,to avoid this capacitor CE is connected in parallel with RE ,it will bypass noise to ground.
9.Which type of biasing is used in RC coupled amplifier?
Ans: Voltage divider ( Potential divider) biasing used in RC coupled amplifier.
10.What is the phase difference between the input and the output of the individual stages and for overall amplifier.
Ans: 1800 is the phase difference between the input and the output of the individual stages and for overall amplifier.
11.What is Cascode amplifier?
Ans: Cascode is two stage amplifier with CE input stage feeds the Common base amplifier.