324 Op Amp

The 324 op amp is a four-channel operational amplifier, and is one of the most popular integrated circuits (ICs) of all time.

Consisting of four operational amplifiers per package, the 324 is a great solution for single supply applications. The negative power supply included in the common mode input and output range eliminates the need for external biasing. This is another significant benefit of the 324 op amp.

The 324 op amp has many different applications, including DC gain blocks, rectifiers, transducer amplifiers, conventional amplifier circuits, etc.

The operational amplifier (or op-amp) is often considered to be a basic building block of analog electronics. Op amps today are almost always found in the form of an integrated circuit, or chip.

Integrated circuits make it possible to manufacture op amps with excellent performance, easy implementation and low cost. They require few peripheral components and the delicate problems of polarization of amplifiers made with discrete components are eliminated. Over time, some well-designed op-amp ICs have become extremely popular, including the 324.

History of the 324 Op Amp

Operational amplifiers were initially developed in the electronic tube era. The first mass-produced op-amp was the K2-W from GAP/R in January 1953.

The first widely available operational amplifier in the form of an integrated circuit (IC) was the Fairchild μA709 bipolar op-amp, created by Bob Widlar in 1965. In 1968, the μA709 was replaced by the μA741, which offered better performance while being more stable and easier to implement.

In 1972, Russell and Frederiksen from the company National Semiconductor introduced an amplifier technique suitable for operation in a single-supply environment at low voltages. The first operational amplifier to use this new technique of operation was the LM324, and it subsequently became the low-cost industry standard general purpose quad op-amp.

LM324 Pinout

The LM324 operational amplifier consists of 14 pins with four op-amps in one package.

Pin description of the 324 operational amplifier

The pins description of the 324 operational amplifier are as follows:

1: output pin of the first op-amp
2: inverter input pin of the first op-amp
3: non inverter input pin of the first op-amp
4: positive supply voltage (VCC)
5: non inverter input pin of the second op-amp
6: inverter input pin of the second op-amp
7: output pin of the second op-amp
8: output pin of the third op-amp
9: inverter input pin of the third op-amp
10: non inverter input pin of the third op-amp
11: ground or negative supply voltage (GND, VEE)
12: non inverter input pin of the fourth op-amp
13: inverter input pin of the fourth op-amp
14: output pin of the fourth op-amp

Pins 4 and 11: the positive and negative voltage supply terminals respectively. The power required to operate the integrated circuit comes from these two pins.

Pins 1, 7, 8 and 14: the output signal that is provided by the internal op-amps is received from these pins. The output voltage received on these pins is based on the feedback approach used and the voltage level on the input pins.

Pins 2, 3, 5, 6, 9, 10, 12 and 13: the input pins of the operational amplifier. Pins 2, 6, 9, 13 are the inverting input pins, while pins 3, 5, 10, and 12 are the non-inverting input pin. Each of the four internal operational amplifiers can be configured separately. When the voltage value at the inverting input pins is greater than the voltage value at the non-inverting input pins, which means the inverting input pins have a high voltage value, the output signal of the corresponding op-amps is low. Similarly, when the voltage value at the non-inverting input pins is greater than the value at the inverting input pins, which means the non-inverting inputs have a high voltage value, then the output signal of the corresponding op-amps is high.

324 Op Amp Packages

The 324 operational amplifier comes mainly in two different packages:

SOP-14: a SOP (Small Outline Package) is a type of surface mount IC package. They are very low-profile (about 1mm) and have tight lead spacing. The 324 operational amplifier in this package has 14 pins and comes in the following dimensions: 5.00 mm length and 4.40 mm width.

DIP-14: a DIP (dual in-line package) is an electronic component package with a rectangular housing and two parallel rows of electrical connecting pins. The 324 operational amplifier in this package has 14 pins and comes in the following dimensions: 19.177 mm length and 6.35 mm width.

SOIC: Small Outline Integrated Circuit, is a surface mount (SMT) integrated circuit package that occupies approximately 30-50% less area than an equivalent Dual In-line Package (DIP), with a typical thickness of 70% or less. The 324 operational amplifier that comes in this package has the following dimension: 8.65 mm length and 3.91 mm width.

How the 324 Op Amp Works

Operational amplifiers usually consist of at least three stages: a differential stage, one or more voltage amplification stages and a voltage buffer.

The differential input stage provides differential amplification between the two inputs as well as the high input impedance.

The amplifier stage is usually a high gain, class A amplifier in order to amplify the signal coming from the differential stage with as little distortion as possible.

The voltage buffer, which serves as an output stage, has a voltage gain of one. It allows the amplifier to provide high output currents with a low output impedance. It also includes current limitations and short circuit protection.

Schematic diagram of the 324 operational amplifier

324 Op Amp Specifications

Here are the main specifications for the LM324 operational amplifier:

Characteristic	Symbol	Value	Unit
Supply Voltage (min-max)	V_CC	3-32	V
Operating Temperature Range	T_OPR	0 to 70	℃
Input offset voltage	V_IO	7 (MAX)	mV
Input offset current	I_IO	150 (MAX)	nA
Common-mode rejection ratio	CMRR	80	dB
Bandwidth	–	1	MHz

Input offset voltage

The input offset voltage of an operational amplifier is a parasitic DC (Direct Current) voltage added to the difference between the input voltages, due to an asymmetry between the characteristics of the internal or external components of the two inputs. In practice, this results in an “unexpected” shift of the output voltage. The input offset voltage of the 324 op amp is 7 mV.

The offset voltage is directly amplified by the circuit. On ICs with a zero setting, this offset can be cancelled by connecting a potentiometer to the appropriate pins. If the operational amplifier is not equipped with zero adjustment pins, it is necessary to use an external circuit to cancel this offset. This way of doing things also makes it possible to get rid of the differences in the offset adjustment mode provided by the manufacturer according to the type of the operational amplifier, and thus to improve interchangeability.

It is worth mentioning that, whatever the method of offset compensation chosen, the offset of these ICs varies with its temperature and some methods can increase this variation or even cancel it.

Input offset current

The input offset current is the difference between the polarization currents flowing through the two inputs. This is the current that must be applied to each of the two inputs so that the output voltage is zero.

Common Mode Rejection Ration (CMRR)

The Common Mode Rejection Ration, or CMRR, is a numerical value that represents the ability of an operational amplifier to reject the common voltage of its two inputs. It is usually expressed in decibels (dB). In practice, the output voltage of an op-amp does not only depend on the voltage difference between these two inputs, but also depends on the average value of the voltages on these two inputs (or common mode voltage).

Bandwidth

The bandwidth corresponds to the frequency range in which the operational amplifier can work with an “acceptable gain”. The higher the gain required of an op-amp, the smaller its bandwidth gets.

Advantages and Disadvantages of the LM324 Op Amp

Advantages of the LM324 Op Amp

The 324 operational amplifier offers many advantages thanks to its internal structure and the low power consumption:

Eliminates the need for dual power supplies.
Four internally compensated operational amplifiers in a single package.
Allows operation directly with voltage close to ground value (0V) and the output voltage can also reach ground value.
Compatible with all forms of logic.
Low current consumption which allows the use of batteries or cells.

Disadvantages of the LM324 Op Amp

Sensitivity to temperature changes: the 324 operational amplifier is suitable for applications in temperatures ranging from -40 to +85 ℃. And the downside here is that any usage of this integrated circuit out of its operating temperature range can lead to a failure because temperature variations cause the base-emitter voltage to change, which directly influences the bias of the transistors.

Narrow bandwidth: the 324 operational amplifier has a bandwidth or frequency range of 1 MHz, which is considered relatively narrow compared to its alternatives, like the LM3900 or the TL074 which have a bandwidth value of 2.5 and 3 MHz respectively.

Applications of the LM324 Op Amp

Oscillator

An oscillator built using an operational amplifier as the active element is called an op-amp oscillator.

Op-amp oscillators are normally used to generate precise and periodic waveforms such as square, sawtooth, triangular and sinusoidal shapes.

One popular type of operational amplifier oscillator is a sinusoidal oscillator. This type of oscillator uses RC (Resistor, Capacitor) or LC (Inductor, Capacitor) circuits that contain adjustable oscillating frequencies, or crystals that have a predetermined oscillation frequency.

These oscillators are circuits created to be unstable. Not the type that is sometimes developed or designed unexpectedly in the lab, but rather types that are deliberately built to continue to be in an unstable or oscillatory state.

Rectifier

An operational amplifier based rectifier is a classical circuit and relies only on a diode and an operational amplifier. This circuit uses a diode in the feedback line and the output of the circuit is taken on the inverting input and not on the output of the operational amplifier. This circuit behaves differently depending on the sign of the input voltage.

This op-amp based rectifier is mainly used in applications like: demodulation of AM signals, peak detector, rectification of low amplitude signals.

Amplifier

An amplifier is used to increase the amplitude of a signal, without changing other parameters of the waveform such as frequency or waveform. Amplifiers are one of the most commonly used circuits in electronics and perform a variety of functions in many electronic systems.

In such application, the op-amp can work as either a non-inverting amplifier or as an inverting amplifier. This arrangement allows to amplify the signal at the input by a defined gain value. The value by which we multiply the input voltage to obtain the output voltage can be deduced from the values of the resistors around its two inputs.

The 324 operational amplifier is used as an amplifier when a high gain op-amp is needed like in audio amplification or in a microphone preamplifier.

Comparator

The op amp comparator is a circuit that has its own reference voltage and compares it with any external input voltage to decide whether the latter is higher or lower than the reference voltage.

Typically, a comparator circuit is used in robots for line following. These line-following robots are specially used in industrial applications for special purposes such as transporting various parts or machines or vehicles by following a specific line from one point to another point. And by using the LM324, conventional operational amplification applications can be implemented very simply.

324 Op Amp Projects

Smartphone detector

This LM324 IC based circuit diagram of cell phone detector is very simple and can detect the cell phone at a distance of 10 to 20 meters. The detection range depends mainly on the cell phone because each mobile has its own signal generation capability. This circuit only detects the coded signal, not its content. Coded signals can be received when the cell phone receives a call, makes a call and when sending and receiving SMS. This circuit can be used for many purposes such as searching for a lost phone, searching for a cell phone in restricted areas.

The circuit is very simple to build using basic electrical and electronic components. The LM324 operational amplifier is the heart of the circuit. This circuit uses only single operational amplifiers of the four operational amplifiers.

A transistor is connected to the output of the operational amplifier to activate the LED and the Piezo buzzer. The circuit can be operated with voltages from 4.5V to 12V DC. The sensitivity of this circuit is fixed, but it can be variable using a 100K variable resistor.

Smartphone detector circuit using an LM324

Voltage comparator

In this type of application, we take advantage of the very high gain of the op-amp, and we let the output have only two possible voltage values: the maximum voltage it can supply, and the minimum voltage it can supply. All intermediate voltages cannot exist in a “stable” way, because the gain is so important here, that the slightest difference in voltage between the two inverting and non-inverting inputs is amplified to such an extent that it can only cancel out the other terminals imposed by the supply voltage. Just imagine a voltage difference of 1 mV, while the gain is 500000, the output will desperately try to reach 500 V… but will obviously not succeed, because the supply voltage is only 15V.

Voltage comparator circuit using an LM324

Alternatives to the 324 Op Amp

LM324B Op Amp

There is an extended family of 324 op amps available. Texas Instruments promotes the LM324B as the ‘next generation’ of the classic LM324 op amp.

Compared with the classic LM324, the LM324B features lower offset voltage, higher supply voltage range, lower input bias current, and a wider temperature range.

LM3900 Op Amp

The LM3900 operational amplifier consists of four independent, high-gain frequency-compensated Norton operational amplifiers whose output voltage is proportional to the difference of the currents applied to the two inputs.

Characteristic	Symbol	Value	Unit
Supply Voltage (Single supply)	V_CC	32 (MAX)	V
Supply Voltage (Dual supply)	V_CC+	16 (MAX)	V
Supply Voltage (Dual supply)	V_CC-	-16 (MAX)	V
Operating Temperature Range	T_OPR	0 to +70	℃
Input offset current	I_IO	200 (MAX)	nA
Bandwidth	–	2.5	MHz

The 3900 operational amplifier has narrow operating temperature range which makes it ideal for applications in normal temperatures. Additionally, it offers wider bandwidth or frequency range.

TL074 JFET Op Amp

The TL074 operational amplifier features junction-gate field-effect transistors (JFET) at the input stage and integrates well-matched high-voltage JFET and bipolar junction transistors (BJT) into a monolithic integrated circuit. The device features high slew rates, low input bias, offset currents, and a low offset voltage temperature coefficient. Low harmonic distortion and low noise make the TL074 op-amp ideal for high-fidelity applications and audio preamplifiers.

Characteristic	Symbol	Value	Unit
Supply Voltage (Single supply)	V_CC	36 (MAX)	V
Supply Voltage (Dual supply)	V_CC+	18 (MAX)	V
Supply Voltage (Dual supply)	V_CC-	-18 (MAX)	V
Output current	Io	1 (MAX)	mA
Bandwidth	–	3	MHz

The main difference between the LM324 and the TL074 is the bandwidth or frequency range, as the TL074 offers wider bandwidth which gives it the ability to work in high-gain applications without losing its frequency range.

LM224 Op Amp

LM224 is a four-channel operational amplifier. This circuits consist of four independent, high gain, internally frequency compensated operational amplifiers. It can operate from both single and split power supplies and the low power supply current drain is independent of the amplitude of the power supply voltage.

Characteristic	Symbol	Value	Unit
Supply Voltage	V_CC	±16 or 32	V
Input Voltage	V_in	-0.3 to Vcc + 0.3	V
Input Current	I_in	50	mA
Operating Temperature Range	T_opr	-40 to +105	℃
Bandwidth	–	1.3	MHz

The LM224 operational amplifier has a wider operating temperature range which makes it preferred to the LM324 for applications in temperatures higher than 80 ℃.

Conclusion – The 324 Op Amp

The 324 op amp is an iconic integrated circuit – one of the most popular ICs of all time. It has four channels and is powered by a single supply on pins 4 and 11.

The LM324 op amp is a very low cost yet effective solution for low voltage, single supply applications. There is an extended 324 family of op amps that greatly enlarge the variety of applications that can be designed for.

If you’d like to learn more about the LM324 family, I’d recommend taking a look at TI’s LM324 product page.