Department of CNET Electronic Circuit II Chapter 2

Department of CNET Electronic Circuit II Chapter 2 Mohammed Abdul Gaffar

Electronic Circuit-II Chapter 2

Topics in the Chapter 2 Ø Operational Amplifier input modes and parameters. Ø Single ended mode OPAMP. Ø Double Ended mode OPAMP. Ø Parameters of OPAMP. Ø Definition of CMRR. Ø Common Mode i/p voltage. Ø I/p offset voltage. Ø Input Bias current. Ø I/p impedance. Ø I/p offset current. Ø Output Impedance. Ø Slew rate.

Operational Amplifier input modes and parameters. Depending on the input signal connection OP-AMP are divided in to two categories. OP-AMP Double Ended Mode Single Ended Mode Inverting Mode Non Inverting Mode Differential Mode Common Mode

Single Ended Mode OP-AMP. • If only one signal is connected to one of the input terminals of OP-AMP and other being grounded then it is called Single ended OPAMP.

Op-Amp Input Modes and Parameters 1. Input Signal Modes – Signal-Ended Input • • When an op-amp is operated in the single-ended mode, one input is grounded and signal voltage is applied only to the other input as shown in Figure. • In the case where the signal voltage is applied to the inverting input as in part (a), an inverted amplified signal voltage appears at the output. • In the case where the signal voltage is applied to the Noninverting input with the inverting input grounded, as in part (b), a Non Inverting amplified signal voltage appears at the output.

Circuit Diagram for Inverting (a) & Noninverting (b) OPAMP.

Double Ended Mode OP-AMP. • If two signals are connected to the two input terminals of OP-AMP then it is called Double ended OP-AMP.

Op-Amp Input Modes and Parameters 2. Input Signal Modes - Differential Input In the Differential Mode, two opposite-polarity (out-of-phase) signals are applied to the inputs, as shown in Figure. This type of operation is also referred to as double-ended. The amplified difference between the two inputs appears on the output.

Op-Amp Input Modes and Parameters 3. Input Signal Modes - Common-Mode Input • In the Common Mode, two signal voltages of the same phase, frequency, and amplitude are applied to the two inputs, as shown in Figure. • When equal input signals are applied to both inputs, they cancel, resulting in a zero output voltage. This action is called common-mode rejection.

Identify the type of input mode for each op-amp in Figure.

Parameters of OP-AMP.

Common-Mode Rejection Ratio The ability of an amplifier to amplify differential signals and reject common-mode signals is called the common-mode rejection ratio (CMRR). CMRR is defined as where Aol is the open-loop differential-gain and Acm is the common-mode gain. CMRR can also be expressed in decibels as

Voltage and Current Parameters VO(p-p): The maximum output voltage swing is determined by the op-amp and the power supply voltages VOS: The input offset voltage is the differential dc voltage required between the inputs to force the output to zero volts IBIAS: The input bias current is the average of the two dc currents required to bias the differential amplifier IOS: The input offset current is the difference between the two dc bias currents

Impedance Parameters ZIN(d) : The differential input impedance is the total resistance between the inputs ZIN(cm) : The common-mode input impedance is the resistance between each input and ground Zout: The output impedance is the resistance viewed from the output of the circuit.

Other Parameters Slew rate: The slew rate is the maximum rate of change of the output voltage in response to a step input voltage Determine the slew rate for the output response to a step input. = 6 V/ms