ECE130.1 LAB 3 Two-Stage Amplifier PDF

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Republic of the Philippines Mindanao State University - Iligan Institute of Technology

COLLEGE OF ENGINEERING & TECHNOLOGY Department of Electrical Engineering and Technology Tibanga, 9200 Iligan City, P.O. Box No.5644 Tel. Nos. (063) 221-4050 loc.4131

ECE130.1 LAB REPORT

Introduction to Analog Integrated Circuits Design Laboratory LAB 3 Two-Stage Amplifier A Laboratory Report Presented to Prof. Aileen Caberos-Gumera Faculty, DEET College of Engineering and Technology, MSU-IIT

SUBMITTED BY: Maagad, Mari Gabriel V. BS-EsE 3

Introduction Amplifiers are an essential component of any endeavor involving signal strength and quality. Audio amplifiers, on the other hand, are used to boost the volume of speech signals and make them more audible by amplifying them and sending them through a speaker. Many applications require performance that a single-stage amplifier cannot provide, necessitating the use of multiple-stage amplification. Because of its high gain and output swing, two-stage operational amplifiers are the most commonly utilized multistage amplifier. The two-stage amplifier circuit has two stages, each of which performs amplification on the incoming audio signals, with the output obtained at the end of the second stage.

Objective The objective of this laboratory exercise is to have a clearer understanding of the designing and process of a Two-Stage Amplifier. Furthermore, we are to vary variables such as adding a resistor and capacitor to differentiate its effects and determine how it affects the circuit’s performance.

Procedure Step 1: From the given circuit structure, simulate differential amplifier and two-stage amplifier respectively and compare the gain, -3dB frequency and gain bandwidth.

Fig. 1. Performance of Two-Stage Amplifier and a Differential Amplifier

Two Stage Amplifier

Differential Amplifier

Gain

-3db

Gain Bandwidth

Two Stage Amp

81dB

51kHz

25MHz

Differential Amp

41dB

10MHz

800MHz

Step 2: Connect the two-stage amplifier as a unit gain buffer, simulate it and observe the stability and output waveform.

Fig. 2. Gain and Phase of Two-Stage Amplifier as a Unit Gain Buffer

Gain

Phase

Fig. 2.1. Slew Rate of Two-Stage Amplifier as a Unit Gain Buffer

Vout

Vinp

From Fig 2, we can observe that the phase margin is less than 0⁰, which shows that the system is unstable. For Fig 2.1, we can observe the input is stable but the output is oscillating which also shows that the system is unstable. Step 3: From the circuit below, simulate the effect of phase margin when adding compensation capacitor.

Fig. 3. Effect of the Phase Margin when Compensation Capacitor is added

Without Cc Gain With Cc=2pF Gain Without Cc Phase

With Cc=2pF Phase

Through the addition of a compensation capacitor, the phase margin improved.

Step 4: Vary the value of compensation capacitor to observe the effect to phase margin and also to observe the effect to slew rate.

Fig. 4. Gain and Phase of Two Stage Amplifier with varied Compensation Capacitor Cc=4pF Gain

Cc=8pF Gain Cc=12pF Gain

Cc=4pF Phase

Cc=8pF P Cc=12pF Phase

Fig. 4.1. Slew Rate of Two Stage Amplifier with varied Compensation Capacitor

Cc=4pF

Cc=8pF

Cc=12pF

We can observe that as the Cc increase, the system becomes more stable while its slew rate decreases. Its slew rate decreases since a larger Cc requires more time to charge or discharge. Step 5: From the circuit below, observe the effect after adding a compensated resistor.

Fig. 5. Effect of the Phase Margin when a Compensated Resistor is added Only Cc With Rc=1.234k and Cc

With Rc=1.234k and Cc

With Rc=6k and Cc

Only Cc

With Rc=6k and Cc

From the simulated results, we can observe that as the Rc increases, the phase margin also increases which results to a more stable system.

Simulation of the Input Common-Mode Range (ICMR), Output Voltage Swing, Common-Mode Rejection Ratio (CMRR), Slew Rate and the Settling Time of the Two Stage Amplifier Circuit:

Fig. 6. Input Common-Mode Range (ICMR) of the Two Stage Amplifier

Vout

ICMR

Vinp

Fig. 6.1. Output Voltage Swing of the Two Stage Amplifier

Vout

Vinp

Fig. 6.2. Common-Mode Rejection Ratio (CMRR) of the Two Stage Amplifier

Ad

Acm

Fig. 6.3. Slew Rate and the Settling Time of the Two Stage Amplifier

Vinp = 1.5v

Vout of Vinp = 1.5v

Vinp = 1v Vout of Vinp = 1v

Fig. 6. Shows the ICMR (Input Common-Mode Range) of the two-stage amplifier in which it is the range of common-mode voltages where it is also in the saturation region thus its gain is almost constant. Fig 6.1 shows the output voltage swing of the two-stage amplifier which indicates the range of output voltage can operate normally. Fig 6.2 shows the CMRR (common-mode rejection ratio) of the two-stage amplifier, it is the ability of rejecting common-mode signal. Fig 6.3 shows the slew rate and the settling time of the two-stage amplifier in which we can observe that as the slew rate increases, the swing of the input pulse also increases.

Questions 1. Why do we use a Common Source structure as the output stage of TwoStage Operational Amplifier? What if we use other structures? We use a Common Source structure as the output stage of Two-Stage Amplifier since it is a transconductance amplifier. A transconductance amplifier has a high input, output impedance, a high voltage gain and a good voltage swing. With these characteristics, it is essential and convenient for amplifying signals. For the CommonGate structure, although it has a high output impedance and high voltage gain but when compared to the common-source structure, the common-source has better characteristics. For the Common-Drain, it has a low output impedance and low voltage gain. Hence the Common-Source structure is more superior than the other two structures.

Hand Calculations:

Conclusion In this lab activity, I have learned more about the characteristics and effects of a two-stage amplifier. Specifically, its effect on its CMRR, ICMR, Slew Rate, Output Swing, Phase Margin Stability, Effects of adding Compensated Capacitor and Resistor and its relation to its voltage gain. Through the laboratory simulations, I have observed that there are trade-offs when varying the parts of the two-stage amplifier. Trade-offs such as high gain but limited output swing or vice versa. Designing a two-stage amplifier really depends on the client’s request or list of specification. We cannot design an ideal two-stage amplifier since there is no such thing as an ideal and we have to adjust and have some trade-offs when designing such amplifier. Compared to the single stage amplifier, the twostage is better in terms of its high gain and high output swing especially when the twostage amplifier is compensated meaning it has the compensated capacitor and resistor. There are a lot of things we need to consider in designing two-stage amplifier. One significant thing we must consider is our phase margin in which we make our phase margin in between the range of 45 degrees to 90 degrees while the optimal is 60 degrees. Things like this, makes designing integrated circuits difficult yet fun. In this time of pandemic, we were not able to do laboratory activities physically and that hinders our learning slightly. Despite of this, I still learned a lot and I think we can fully understand a concept when we actually experience it first-hand. Nevertheless, this lab activity made me learn more and it was challenging and fun.

References ● Lab 3 Two-Stage Amplifier Powerpoint given by Ma’am Aileen...