LM13700 OTA IC: Pinout, Specs, Applications & Circuit Guide

Introduction

The LM13700 is a two-device transconductance amplifier (OTA) integrated circuit that has been a popular analog electronics application for decades. It is very important in voltage-controlled circuits, audio signal processing, synthesizers, and high-speed analog control systems. An OTA differs in its response to an input voltage in that, unlike traditional types of operational amplifiers that generate a voltage output proportional to the difference between two input voltages, an OTA generates a current proportional to the input voltage. This special feature allows the flexible electronic control of gain, frequency and signal dynamics with a simple bias current. Thanks to its versatility, stability, and excellent performance-to-cost ratio, the LM13700 remains a favorite choice among engineers, hobbyists, and audio designers.

 

What Is the LM13700 OTA IC?

The LM13700 is a monolithic two-port operation transconductance amplifier that is used to supply gain that is electronically controllable. Both of the same two OTAs within the IC convert a differential input voltage to a single-ended output current, which may be converted to a voltage with an external load resistor. An external bias current is required to vary the transconductance of the amplifier and thus its gain, such that it is ideal in voltage-controlled amplifiers, filters, oscillators, and modulators.

 

Basic Operating Principle of OTA

An OTA is a simple device that produces a proportional current in the output as the difference in input voltage decreases, and also in correlation with the bias current. The fundamental relationship is expressed as:

 

Gm = Iabc / 2VT

 

In which Gm is the transconductance, Iabc is the current in the bias control, and VT is the thermal voltage. This connection makes it possible to accurately tune the circuit gain, filter cutoff frequency or oscillator frequency by changing the bias current.

 

Key Functional Blocks Inside LM13700

Internally, the LM13700 integrates a differential input stage, current mirrors, linearizing diodes, and output buffer amplifiers. The diodes are linearized to a much greater extent, and the integrated output buffers make the circuit-design extremely easy and enhance the ability of their load-driving. The dual-channel structure allows the IC to implement stereo or differential circuits within a single compact package.

 

LM13700 Pinout and Package Details

LM13700 is normally packaged in 16-pin DIP and SOIC devices and is therefore applicable to both prototyping and commercial designs.

 

LM13700 Pin Configuration and Functions

Each OTA inside the LM13700 includes differential inputs, bias current control pins, linearizing diode connections, and output terminals. The main pin functions include:

 

• Non-inverting and inverting inputs for signal processing
• Bias current control pins for gain adjustment
• Linearizing diode pins for distortion reduction
• Buffered voltage outputs
• Power supply pins for dual or single-supply operation

 

Package Types, Dimensions, and Footprints

The DIP-16 package is suitable for breadboards and educational designs, whereas the SOIC-16 is more suitable for small PCBs. Footprint guidelines must be adhered to closely by the designers in order to reduce parasitic capacitance and noise collection.

 

LM13700 Electrical Specifications

LM13700 has a broad operating temperature and constant electrical behavior that can be applied in the audio and industrial fields.

 

Absolute Maximum Ratings

The maximum supply voltage typically ranges up to ±18 V, with strict limits on input currents and power dissipation. Exceeding these values may result in permanent device damage.

 

Recommended Operating Conditions

Typical operation occurs between ±5 V and ±15 V supply voltages. The bias current may vary between several milliamps and microamps, and this enables the performance of the circuit to be dynamically controlled.

 

Key Performance Parameters

The main parameters are low input offset voltage, a large range of transconductance, low distortion, medium noise, and a large compliance voltage of the output. These features render the LM13700 usable in harsh analog signal processing.

 

How the LM13700 Works (Internal Architecture)

The LM13700 is a two-in-one integrator with OTAs and has bias control and an output buffer for each. This dual configuration allows flexible stereo and differential signal processing.

 

Dual OTA Configuration Explained

All channels may be used singly or in combination, allowing balanced circuits, state-variable filters and stereo audio effects with one IC.

 

Linearizing Diodes and Their Function

The integrated diodes enhance linearity by adjusting the nonlinear exponential properties of transistor junctions of the bipolar, and the harmonic distortion is minimized greatly.

 

Output Buffers and Signal Conditioning

Built-in buffers allow the OTA output current to be converted into a voltage with minimal external components, simplifying design and enhancing signal integrity.

 

Typical LM13700 Application Circuits

The LM13700 is extensively used in voltage-controlled and analog signal processing circuits.

 

Voltage-Controlled Amplifier (VCA) Circuits

Audio signal levels can be controlled with electronic accuracy using VCAs constructed using the LM13700, and find regular use in compressors, limiters and synthesizer modules.

 

Voltage-Controlled Filter (VCF) Circuits

By controlling transconductance, the LM13700 enables voltage-controlled cutoff frequency in low-pass, high-pass, and band-pass filter circuits.

 

Voltage-Controlled Oscillator (VCO) Circuits

The LM13700 is commonly used to generate sine, triangle, and sawtooth waveforms in analog synthesizers, with frequency controlled by bias current.

 

Audio Effects Circuits

Phasers, flangers, tremolo units, and wah pedals frequently use LM13700-based designs to achieve smooth dynamic modulation.

 

Analog Signal Processing Applications

Applications include modulators, demodulators, envelope detectors, AGC loops, and sensor signal conditioning.

 

LM13700 Circuit Design Guide

Stability, low noise and minimum distortion make sure that they are properly designed.

 

Bias Current Selection and Gain Control

Selecting the appropriate bias current is critical for balancing gain, linearity, and power consumption. Voltage references of precision current sources or controlled by resistors are commonplace.

 

Input Signal Conditioning Techniques

AC coupling capacitors, impedance matching networks, and proper DC biasing help maintain signal integrity and prevent distortion.

 

Output Stage Design and Loading Considerations

Buffer amplifiers, RC filters, and impedance-matching resistors optimize signal delivery and reduce noise coupling.

 

Noise Reduction and Distortion Optimization

Even short signal paths, star grounding, high-quality capacitors and shielding methods make significant contributions to better performance.

 

Common LM13700 Example Circuits

Simple VCA Circuit Example

A basic VCA can be built using one OTA channel, a bias current source, and a load resistor, allowing real-time gain control via an external control voltage.

 

State-Variable Filter Circuit Example

With both OTAs, multifunction filters with low-pass, high-pass, and band-pass simultaneous outputs can be created by designers.

 

Triangle and Sine Wave Generator Circuit

Oscillator designs using LM13700 provide stable waveform generation suitable for audio synthesis and test signal generation.

 

LM13700 vs Common Alternative OTA ICs

LM13700 vs CA3080

LM13700 is superior in linearity, distortion and two-channel integration compared to the older CA3080.

 

LM13700 vs LM13600

LM13700 is an improved form of the LM13600, which offers better performance, better buffers and better distortion properties.

 

LM13700 vs Modern OTA Solutions

Although modern ICs can provide digital control and reduce noise, the LM13700 still cannot be found to be inferior in ease of use, versatility, and analog realism.

 

Practical Troubleshooting and Design Tips

Common Circuit Problems and Solutions

Problems like distortion, oscillation instability and noise can usually be improved by bias control, optimization of layout, and filtering.

 

Debugging and Measurement Techniques

With oscilloscopes, spectrum analyzers and signal generators, it is possible to diagnose and fine-tune circuit behavior.

 

FAQs About LM13700 OTA IC

What is the main function of the LM13700?

It offers transconductance, which is electronically controllable on voltage-controlled circuits.

 

How does an OTA differ from a normal op amp?

An OTA outputs current instead of voltage and allows gain control via bias current.

 

What supply voltage does LM13700 require?

It typically operates from ±5 V to ±15 V supplies.

 

Is LM13700 suitable for synthesizer circuits?

Yes, it is one of the most popular ICs in analog synthesizer designs.

 

Conclusion

LM13700 OTA IC is currently one of the most flexible and powerful analog building blocks. Its ability to provide voltage-controlled amplification, filtering, and oscillation makes it indispensable in audio electronics, synthesizer modules, and analog signal processing systems. The LM13700 has great performance, reliability and flexibility when properly designed and laid out on the circuit board; hence its future applicability in the current electronic designs.

 

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