Analogue Electronic 2 EMT 212 Chapter 1 Operational Amplifier By En. Rosemizi B. Abd Rahim

1.0 Operational Amplifier 1.1 Introduction 1.2 Ideal Op-Amp 1.3 Op-amp input modes 1.4 Op-amp Parameters 1.5 Operation Single-mode Differential-mode Common-mode operation 1.6 Op-Amps basics 1.7 Datasheet

1.1 Introduction Typical IC packages IC packages placed on circuit board

1.1 Introduction Uses of Op-Amp To provide voltage amplitude changes (amplitude and polarity) Comparators Oscillators Filter circuits Instrumentation circuits

1.1 Introduction Definition The operational amplifier or op-amp is a circuit of components integrated into one chip. A typical op-amp is powered by two dc voltages and has an inverting(-) and a non-inverting input (+) and an output. Op-amps were used to model the basic mathematical operations ; addition, subtraction, integration, differentiation etc in electronic analog computers.

1.1 Introduction Two Power Supply +V : Positive PS -V : Negative PS One Output Terminal Op-amp schematic symbol Two Input Terminal Inverting input Non-inverting input

1.2 Ideal Op-Amp Practical Op-Amp Ideal Op-Amp

1.2 Ideal Op-Amp Properties Practical Op-Amp Ideal Op-Amp input impedance 500k-2M output impedance 20-100  open-loop gain (20k to 200k) Bandwidth limited (a few kHz) noise contribution Non-zero DC output offset Infinite input impedance Zero output impedance Infinite open-loop gain Infinite bandwidth Zero noise contribution Zero DC output offset Both differential inputs stick together

1.2 Ideal Op-Amp Infinite Input Impedance Input impedance is measured across the input terminals It is the Thevenin resistance of the internal connection between the two input terminals. Input impedance is the ratio of input voltage to input current. Zi=(Vi/Ii) When Zi is infinite, the input current is zero. the op amp will neither supply current to a circuit nor will it accept current from any external circuit. In real, the resistance is 500k to 2M

1.2 Ideal Op-Amp Zero Output Impedance Looking back into the output terminal, we see voltage source with an internal resistance. The internal resistance of the op-amp is op-amp output impedance This internal resistance is in series with the load, reducing the output voltage available to the load Real op-amps have output impedance in the range 20-100  .

1.2 Ideal Op-Amp Infinite Open-Loop Gain Open-Loop Gain, A is the gain of the op-amp without feedback. In the ideal op-amp, A is infinite In real op-amp is (20k to 200k)

1.2 Ideal Op-Amp Infinite Bandwidth The ideal op-amp will amplify all signals from DC to the highest AC frequencies In real op-amps, the bandwidth is rather limited This limitation is specified by the Gain-Bandwidth product, which is equal to the frequency where the amplifier gain becomes unity Some op-amps, such as 741 family, have very limited bandwidth up to a few kHz

1.2 Ideal Op-Amp Zero Noise Contribution in an ideal op amp, all noise voltages produced are external to the op amp. Thus any noise in the output signal must have been in the input signal as well. the ideal op amp contributes nothing extra to the output noise.

1.2 Ideal Op-Amp Zero Output Offset The output offset voltage of any amplifier is the output voltage that exists when it should be zero. The voltage amplifier sees zero input voltage when both inputs are grounded. This connection should produce a zero output voltage. If the output is not zero then there is said to be an output voltage present. In the ideal op amp this offset voltage is zero volts, but in practical op amps the output offset voltage is nonzero.

1.2 Ideal Op-Amp Both Differential Inputs Stick Together this means that a voltage applied to one inverting inputs also appears at the other non-inverting inputs. If we apply a voltage to the inverting input and then connect a voltmeter between the non-inverting input and the power supply common, then the voltmeter will read the same potential on non-inverting as on the inverting input.

1.3 Op-Amp input Modes Single-Ended input mode input signal is connected to one input and the other input is grounded. input signal at +ve terminal  output same polarity as the applied input signal input signal at –ve terminal  output opposite in phase to the applied input signal

1.3 Op-Amp input Modes Differential mode input two out-of-phase signals are applied with the difference of the two amplified and produced at the output.

1.3 Op-Amp input Modes Common mode input two signals of same phase, frequency, and amplitude are applied to the inputs which results in no output (signals cancel). Practically, a small output signal will result. This is called common-mode rejection. This type of mode is used for removal of unwanted noise signals.

1.4 Op-Amp Parameters Common-Mode Rejection Ratio (CMRR) The ability of amplifier to reject the common-mode signals Ratio of open-loop gain to common-mode gain The higher the CMRR, the better open-loop gain is high and common-mode gain is low.

1.4 Op-Amp Parameters Common-Mode Input Voltage The range of input voltages which, when applied to the both inputs, will not cause clipping or other output distortion. Input Offset Voltage The differential dc voltage required between the inputs to force the output to zero volts. Range between 2 mV

1.4 Op-Amp Parameters Input Bias Current The dc current required by the inputs of the amplifier to properly operate the first stage. Is the average of both input currents

1.4 Op-Amp Parameters Input Impedance Is the total resistance between the inverting and non-inverting inputs. Differential input impedance is measured by the changes of differential input voltage over changes of bias current. Common-mode input impedance is measured by the changes of common-mode input voltage over changes of bias current.

1.4 Op-Amp Parameters Input Offset Current Is the different of input bias currents Input offset current error offset voltage

1.4 Op-Amp Parameters Output Impedance Is the resistance viewed from the output terminal of the op-amp.

1.4 Op-Amp Parameters Slew Rate Is the maximum rate of change of the output voltage in response to a step input voltage.

1.4 Op-Amp Parameters Example Determine the slew rate

1.5 Operation Differential Amplifier Circuit Basic amplifier circuit If an input signal is applied to either input with the other input is connected to ground, the operation is referred to as ‘single-ended.’ If two opposite-polarity input signals are applied, the operation is referred to as ‘double-ended.’ If the same input is applied to both inputs, the operation is called ‘common-mode.’

1.5 Operation Differential Amplifier Circuit DC Analysis DC bias of differential amplifier circuit DC Analysis

1.5 Operation Differential Amplifier Circuit Example Solution Calculate the dc voltages and currents

1.5 Operation Differential Amplifier Circuit AC Analysis Single-Ended AC equivalent of differential amplifier circuit AC connection of differential amplifier

1.5 Operation Differential Amplifier Circuit AC Analysis Single-Ended AC equivalent circuit connection to calculate Av1 = Vo1 / Vi1

1.5 Operation Differential Amplifier Circuit AC Analysis - Single ended KVL Scan figure 10.11 & 10.15 Partial circuit for calculating Ib

1.5 Operation Differential Amplifier Circuit Example Solution Calculate the single-ended output voltage Vo1

1.5 Operation Differential Amplifier Circuit AC Analysis - Double ended A similar analysis can be used to show that for the condition of signals applied to both inputs, the differential voltage gain magnitude is

1.5 Operation Differential Amplifier Circuit AC Analysis - Common-mode Common-mode connection

1.5 Operation Differential Amplifier Circuit AC Analysis - Common-mode

1.6 Op-Amp Basics Basic Op-Amp Op-amp equivalent circuit practical ideal

1.6 Op-Amp Basics Basic Op-Amp - Constant-gain multiplier input voltage at minus output voltage opposite in phase

1.6 Op-Amp Basics Basic Op-Amp - Constant-gain multiplier Op-amp ac equivalent circuit

1.6 Op-Amp Basics Basic Op-Amp - Constant-gain multiplier Ideal Op-amp equivalent circuit Redrawn equivalent circuit

1.6 Op-Amp Basics Basic Op-Amp - Constant-gain multiplier Using Superposition theorem i) V1 only (set –AvVi =0) ii) –AvVi only (set V1 =0) Shown that the ratio i/o depends only on the value of Rf and R1

1.6 Op-Amp Basics Basic Op-Amp - Unity Gain If Rf = R1 Shown that the output voltage equal to input voltage with 180º phase inversion.

1.6 Op-Amp Basics Basic Op-Amp - Constant Magnitude Gain If Rf = 10R1 Shown that the output voltage equal to 10x input voltage with 180º phase inversion.

1.7 Data Sheet LM741

1.7 Data Sheet LM741

1.7 Data Sheet LM741

1.7 Data Sheet LM741

1.7 Data Sheet LM741

1.7 Data Sheet LM741