LM13700 Dual Operational Transconductance Amplifier (OTA)

Overview

The LM13700 is a dual operational transconductance amplifier (OTA) that provides two independent current-controlled transconductance amplifiers in a single package. Each amplifier features differential inputs and a push-pull output, making it highly versatile for analog signal processing applications. The device is designed with linearizing diodes at the inputs to minimize distortion and accommodate higher input levels, resulting in a 10 dB improvement in signal-to-noise ratio (SNR) at 0.5% total harmonic distortion (THD). The LM13700 also includes high-impedance buffers optimized to complement the dynamic range of the amplifiers.

Unlike its predecessor, the LM13600, the LM13700 features output buffers with input bias currents (and consequently output DC levels) that are independent of the amplifier bias current (I_ABC). This enhancement makes the LM13700 particularly suitable for high-performance audio applications where DC offset and bias current stability are critical.

Features

• Dual Independent OTAs: Contains two current-controlled transconductance amplifiers in a single package.
• Linearizing Diodes: Reduces distortion and allows for higher input signal levels, improving SNR by 10 dB at 0.5% THD.
• High-Impedance Buffers: Optimized to match the dynamic range of the amplifiers.
• Wide Transconductance Adjustment Range: Adjustable over six decades, providing precise control over gain and response.
• Improved Output Buffers: Input bias currents (and DC output levels) are independent of I_ABC, enhancing performance in audio applications.
• Differential Inputs: Enables balanced signal processing and common-mode noise rejection.
• Push-Pull Outputs: Provides symmetrical output drive capability.
• Shared Supply Pins: Simplifies power supply routing while maintaining independent amplifier operation.

Applications

The LM13700 is widely used in analog signal processing and modulation applications due to its flexible transconductance control and low distortion characteristics. Key applications include:

• Voltage-Controlled Amplifiers (VCAs): Used in audio mixers, synthesizers, and dynamic range compression circuits.
• Voltage-Controlled Filters (VCFs): Employed in parametric equalizers and synthesizer filter modules.
• Analog Multipliers and Modulators: Facilitates amplitude modulation (AM), frequency modulation (FM), and ring modulation.
• Automatic Gain Control (AGC) Circuits: Maintains consistent signal levels in communication and audio systems.
• Current-Controlled Oscillators: Used in waveform generation and frequency modulation applications.
• Audio Processing: Enhances performance in distortion effects, dynamic range control, and tone shaping circuits.

Electrical Characteristics

The following table summarizes the key electrical specifications of the LM13700 under typical operating conditions (unless otherwise noted):

Absolute Maximum Ratings

• Supply Voltage (V₊ to V_-): ±18V
• Differential Input Voltage: ±5V
• Amplifier Bias Current (I_ABC): 2 mA maximum
• Operating Temperature Range: 0°C to +70°C
• Storage Temperature Range: -65°C to +150°C

Typical Operating Characteristics

• Transconductance (g_m) Range: Adjustable from 0 to ~10 mS (millisiemens)
• Input Bias Current (Linearizing Diodes): 0.5 µA typical
• Output Buffer Input Bias Current: 0.1 µA typical (independent of I_ABC)
• Total Harmonic Distortion (THD): 0.5% at 10 dB SNR
• Common-Mode Rejection Ratio (CMRR): 90 dB typical
• Bandwidth (Small Signal): 2 MHz typical

Package Information

The LM13700 is available in multiple package options to accommodate different assembly and thermal requirements. The most common package is the 16-pin dual in-line package (DIP) and surface-mount SOIC-16.

16-Pin DIP (Dual In-Line Package)

• Package Type: PDIP-16
• Dimensions: 19.3 mm x 6.35 mm (0.76 in x 0.25 in)
• Pin Pitch: 2.54 mm (0.1 in)
• Material: Molded plastic

16-Pin SOIC (Small Outline Integrated Circuit)

• Package Type: SOIC-16
• Dimensions: 9.9 mm x 3.9 mm (0.39 in x 0.15 in)
• Pin Pitch: 1.27 mm (0.05 in)
• Material: Plastic, surface-mount compatible

Conclusion

The LM13700 is a highly versatile dual operational transconductance amplifier that offers exceptional performance in analog signal processing applications. Its linearizing diodes, wide transconductance adjustment range, and improved output buffers make it ideal for audio processing, modulation, and filtering circuits. Available in both through-hole and surface-mount packages, the LM13700 provides designers with flexibility in system integration while maintaining high fidelity and low distortion characteristics.