Differenential amplifier design and characterisation
- 1. Experiment-6 Differential Amplifier Electronics Circuits Lab Group- 12 Submitted by - Name: Sreedeep Chatterjee Roll No: 23IE10046
- 2. Objective • To understand operation of a fully differential amplifier with tail resistor • To design and simulate a fully differential amplifier with tail resistor
- 4. Part (i) calculation • Given Vce = 5V, taking Ic = 1.5mA Thus Ic*(Re+Rc) = Vcc-5V = 7V Re + Rc = 7V/1.5mA = 4.67k ohm • Given Vb = 2V Vb – Vbe = 2V – 0.7V = 1.3V = Ve Ve/Rc = Ic = 1.5mA Rc = 0.87k ohm Re = 3.8k ohm Since the differential Amplifier is symmetric, we can use these results on both sides
- 5. Calculations continued • Vb = 2V using Vcc*(Rb/(Ra+Rb)) = Vb • Given, bias current ~ 10 times base terminal current Taking Ib = Ic/beta = 1.5mA/200 = 7.5µA Thus I*Rb = 2V Rb = 27k ohm Calculating for Ra gives – Ra = 135k ohm
- 6. LTspice • The circuit used in the simulation is as such • When needed the emitter of both transistors was shorted for switch closed state
- 7. Part (ii) operating point with sw open • Vo1 – Ve = Vce = 5.27V • Ic = 1.5mA • Both are consistent with required DC operating point
- 8. Operating point with sw closed • Vce = Vo1 – Ve = 5.27V • Ic = 1.5mA • Both are consistent with required values of DC operating point
- 9. Part (iii) 3kHz with sw open • Input = 80mV p-p • Output = 480mV p-p Out of phase Gain = 6
- 10. Part (iv) 3kHz with sw closed • Input and output are out of phase • Gain is much higher
- 11. Part (v) pseudo differential sweep sw open
- 12. Part (v) pseudo differential sweep sw closed
- 13. Part (vi) differential mode 3 kHz sw open
- 14. Sw closed
- 15. Part (vii) Common Mode input
- 16. Part (vii) Common Mode output Amplitude is approx. 0.22V p-p
- 17. Part (viii) differential sweep sw open
- 18. Part (viii) differential sweep sw closed
- 19. Part (ix) common mode sweep In range of <-20dB therefore we can observe that common mode gain is negligibly small
- 20. Part (xi) adding Vc to differential input Here the red wave is the Input given, Vi1 is the Point beyond the Capacitor, thus the Capacitor is correctly Removing the dc part Of the source and dc op. Point is maintained The other input (i.e Vc – Vd/2) is the but Out of phase The input is at 1kHz
- 21. Output Output is consistent With previous results
- 22. Conclusion • In Part A of the experiment, we effectively developed and examined a differential amplifier utilizing a tail resistor to achieve stable biasing. This resistor played a crucial role in establishing the correct operating point and promoting equal current flow through the transistors. Both theoretical analysis and experimental results validated that the tail resistor helps sustain stable bias conditions across varying scenarios while also improving the amplifier’s ability to reject common-mode signals. The overall performance of the circuit exhibited strong differential gain and linearity, highlighting its reliability for precision and stable applications.
- 23. Key Takeaways • Bias Stability: The inclusion of the tail resistor significantly contributes to maintaining a steady bias current, ensuring that both transistors function within their ideal operating regions. • Enhanced Common-Mode Rejection: By integrating the tail resistor, the differential amplifier achieves improved suppression of common-mode signals, which is vital for minimizing unwanted noise and external disturbances. • Gain Regulation: The experiment underscored how emitter degeneration—modulated by the tail resistor— impacts the amplifier’s gain, offering key insights into designing circuits that strike a balance between amplification, linearity, and stability. • Design Considerations: Optimizing amplifier performance involves carefully navigating the trade-offs between gain, stability, and linear response. The tail resistor plays a central role in fine-tuning these parameters. • Real-World Application: Experimental observations aligned closely with theoretical expectations, reinforcing the importance of deliberate component choices and thoughtful circuit design in achieving dependable amplifier performance.