Operational Amplifiers Lesson 1 PDF

Operational Amplifiers Lesson 1 9/14/2021 ECMIXS30 - MALAAY - 2021 2 Outline of Topic 1. Introduction to Operational Amplifiers 2. Op-amp input modes and parameters 3. Op-amps with negative feedback 4. Effects of negative feedback on op-amps impedances 5. Bias current and...

Operational Amplifiers Lesson 1 9/14/2021 ECMIXS30 - MALAAY - 2021 2 Outline of Topic 1. Introduction to Operational Amplifiers 2. Op-amp input modes and parameters 3. Op-amps with negative feedback 4. Effects of negative feedback on op-amps impedances 5. Bias current and offset voltage compensation 6. Open and closed loop response 7. System application 9/14/2021 ECMIXS30 - MALAAY - 2021 3 Introduction to Operational Amplifiers Lesson 1.1 9/14/2021 ECMIXS30 - MALAAY - 2021 4 Introduction to Operational Amplifiers (Op-Amps) Op-amps are primarily used to perform mathematical operations such as addition, subtraction, integration, and differentiation. Before, op-amps were constructed with vacuum tubes which works on high voltages. Now, op-amps are linearly constructed in integrated circuits (ICs) that use low DC voltages which are considered reliable and inexpensive. 9/14/2021 ECMIXS30 - MALAAY - 2021 5 Introduction to Operational Amplifiers (Op-Amps) 9/14/2021 ECMIXS30 - MALAAY - 2021 6 Symbols and Terminals A standard op-amp has two (2) input terminals: 1. Inverting Terminal (-) 2. Non-inverting Terminal (+) A standard op-amp has only one (1) output and can be operated with DC supply voltages: 1. Positive terminal 2. Negative terminal 9/14/2021 ECMIXS30 - MALAAY - 2021 7 The Ideal Op-Amp These op-amps do not meet ideal standards but is easier to understand. Used particularly for analysis of a device in an ideal point of view. Basic characteristics: 1. Infinite voltage gain 2. Infinite bandwidth 3. Infinite input impedance (open circuit) 4. Zero output impedance 9/14/2021 ECMIXS30 - MALAAY - 2021 8 The Ideal Op-Amp 9/14/2021 ECMIXS30 - MALAAY - 2021 9 The practical Op-Amp Since an ideal device can never be made because of its limitations, a practical op-amp should be constructed for practical applications. Measurements and results can be compared to an ideal device for accurate adjustments and tweaking. Basic characteristics: 1. Very high voltage gain 2. Wide bandwidth 3. Very high input impedance 4. Very low output impedance 9/14/2021 ECMIXS30 - MALAAY - 2021 10 The practical Op-Amp 9/14/2021 ECMIXS30 - MALAAY - 2021 11 Internal block diagram of an Op-Amp A typical op-amp has three (3) types of amplifier circuit: 1. Differential amplifier – input stage, difference voltage between inputs 2. Voltage amplifier – class A amplifier, for additional gain 3. Push-pull amplifier – class B amplifier, for output only 9/14/2021 ECMIXS30 - MALAAY - 2021 12 Differential Amplifier (Input Stage) Differential amplifier forms the input stage of the op-amp. Differential – ability of the amplifier to amplify the difference of two input signals applied to its inputs. The difference of the input signals are amplified. If there is no difference, then the output is zero (0). 9/14/2021 ECMIXS30 - MALAAY - 2021 13 Differential Amplifier (Input Stage) 9/14/2021 ECMIXS30 - MALAAY - 2021 14 Op-Amp Input Modes and Parameters Lesson 1.2 9/14/2021 ECMIXS30 - MALAAY - 2021 15 Input Signal Modes Recall: The inputs signals are determined by the first stage which is a differential amplifier. Types: 1. Single-ended mode 2. Differential mode 3. Common mode 9/14/2021 ECMIXS30 - MALAAY - 2021 16 Single-Ended Mode One input grounded, one input connected to the voltage supply. Two (2) cases: 1. If voltage is applied at the inverting input, the inverted amplified signal voltage can be measured at the output. (b) 2. If the voltage is applied at the non-inverting input, the non-inverted amplified signal voltage can be measured at the output. (a) 9/14/2021 ECMIXS30 - MALAAY - 2021 17 Single-Ended Mode 9/14/2021 ECMIXS30 - MALAAY - 2021 18 Differential Mode Two opposite-polarity signals (out-of-phase) are applied to the inputs. Also referred to as double-ended mode. The amplified difference between the two (2) inputs can be measured at the output. 9/14/2021 ECMIXS30 - MALAAY - 2021 19 Differential Mode 9/14/2021 ECMIXS30 - MALAAY - 2021 20 Common Mode Two signal voltages are in-phase and applied to the input. When equal input signals are applied to both inputs, it results to a zero output voltage. This occurrence is called common-mode rejection. Importance: If there are unwanted signals on both inputs, then it will not appear at the output and will be distorted. 9/14/2021 ECMIXS30 - MALAAY - 2021 21 Common Mode 9/14/2021 ECMIXS30 - MALAAY - 2021 22 Common Mode Rejection Ratio (CMRR) Unwanted signals that appears on common mode are distorted and being cancelled by the op-amp so that it will not appear on the output. The measure of an op-amp’s ability to reject common mode signals is a parameter called common mode rejection ratio (CMRR). → Unitless value → Unit in Decibel (dB) value 9/14/2021 ECMIXS30 - MALAAY - 2021 23 Example 1 9/14/2021 ECMIXS30 - MALAAY - 2021 24 Common Mode Input Voltage Range ± 10 V to ± 15 V (DC supply) – applied to both inputs Not within the voltage range: output will be clipped or distorted. Tip: Common Mode Input Voltage Range can be identified in the specifications sheet of an op-amp (IC). 9/14/2021 ECMIXS30 - MALAAY - 2021 25