IC-Mart Your Trusted Source for Transconductance Amplifiers IC Chips

(from leading manufacturers)

Global OTA Manufacturers and Representative Models

1. Texas Instruments (TI / includes National Semi & Burr-Brown)

TI offers the industry’s most comprehensive OTA lineup, from general audio to ultra-high-speed RF models.

• General Purpose: LM13700 / LM13700N. This is the industry-standard dual-channel OTA. It includes output buffers and linearization diodes.
• High Speed / Wide Bandwidth:
  • OPA861: Ultra-high-speed single-channel OTA (80 MHz bandwidth). Ideal for video, sample-and-hold, and RF front-ends.
  • OPA860: Wideband OTA with an open-loop buffer (470 MHz bandwidth).
  • OPA2662: Dual-channel, 370 MHz wide-bandwidth OTA.
• Classic Models: LM3080. A classic single-channel OTA. Most modern designs now use the LM13700.

2. Analog Devices (ADI / includes Maxim & Linear Tech)

ADI focuses on high performance, precision, and specific functional integration, such as OTAs with AGC control.

• High Speed & Specialized Control:
  • LT1228: 100MHz current feedback OTA. It features an integrated current feedback amplifier (CFA) for voltage-controlled gain.
  • MAX435: Wideband OTA with differential output. Used for high-speed signal distribution.
• Precision / Low Voltage:
  • MAX4132: Low voltage, low noise, Rail-to-Rail amplifier. Used for transconductance conversion in precision loops.
  • LT1252: Low-cost, high-speed video OTA.

3. ON Semiconductor (onsemi)

Onsemi focuses on general-purpose replacements for the industrial and audio markets.

• Industrial Standard:
  • NE5517 / NE5517D: Classic dual-channel OTA. It is a direct competitor to the LM13700. Widely used in electronic instruments and audio circuits.
  • AU5517: Automotive-grade version of the NE5517 (AEC-Q100 compliant).

4. STMicroelectronics (ST)

ST provides low-power models in specialized packages for consumer electronics.

• Representative Model: TS921. Often classified as a standard op-amp, but used for signal conversion in low-voltage (from 2.7V) applications due to its transconductance traits.

5. Renesas / Intersil

Maintains classic precision OTA products for medical and legacy industrial equipment.

• Representative Model: CA3080 / CA3080E. Historically the most famous single-channel OTA. While marked as “Obsolete,” stock is often available through authorized distributors like Mouser or Rochester.

Manufacturer	Core Model	Key Selling Point	Recommended Package
TI	LM13700	Most versatile, dual-channel	SOIC-16, DIP-16
TI	OPA861	Ultra-high bandwidth, RF suited	SOT-23-6
onsemi	NE5517	Cost-effective, Audio/Industrial	SOIC-16
ADI	LT1228	Integrated CFA, powerful features	SO-8
ADI	MAX435	Differential output, high stability	SOIC-14

Chinese OTA Manufacturers and Representative Models

1. HGsemi

A well-known domestic manufacturer for “direct replacements” of TI and onsemi models.

• Model: HGLM13700.
• Features: Direct equivalent to TI’s LM13700. Dual-channel with integrated buffers.
• Apps: Industrial control, audio filters, AGC.

2. SGMICRO

A leader in Chinese analog ICs. SGMICRO uses high-performance Variable Gain Amplifiers (VGA) or current feedback amplifiers to meet high-frequency needs.

• Model: SGM450 / SGM452 (VGA).
• Features: Superior high-frequency response and dynamic range compared to older OTAs.
• Apps: Base stations, medical ultrasound, high-speed signal chains.

3. Slkor

Active in replacing TI and NXP brands with a large portfolio of general analog ICs.

• Model: SL13700.
• Features: Domestic LM13700 version. Fully compatible in package and parameters.
• Apps: Audio synthesizers, voltage-controlled amplifiers.

4. Analoguetek

Focuses on high-performance analog front-ends for high-bandwidth scenarios.

• Model: High-speed Buffers or Current-mode Amplifier series.
• Features: High slew rate and bandwidth. Replaces ADI or TI high-speed OTA series.

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Understanding the Transconductance Amplifier IC

Transconductance (g_m) is the ratio of output current change to input voltage change:

g_m = \Delta I_{out} / \Delta V_{in}

Units are usually mA/V or mS (millisiemens).

Three Core Characteristics:

1. Voltage Controlled Current Source (VCCS): It acts as a current source controlled by voltage.
2. Adjustable Transconductance: You can dynamically change the gain ($g_m$) by varying the bias current ($I_{abc}$) at a specific pin.
3. High Output Impedance: Unlike standard op-amps, OTAs have very high output impedance.

Typical Application Scenarios

• Audio & Synthesizers: Classic use cases include Voltage Controlled Amplifiers (VCA), Filters (VCF), and Oscillators (VCO).
• Automatic Gain Control (AGC): OTAs stabilize output signals in receivers or microphones by adjusting gain based on input strength.
• High-Speed Sample and Hold: OTAs use high output impedance to quickly charge capacitors and prevent leakage, ensuring precise sampling for ADCs.
• Modulation & Demodulation: Used as multipliers for Amplitude Modulation (AM) and signal recovery in communications.
• Industrial V/I Conversion: Converts weak sensor voltages into standard 4-20mA current signals for interference-free long-distance transmission.
• Neuromorphic Computing: Simulates synaptic weights in analog AI chips through current-regulated gain.

OTA Classifications

1. General Purpose: Dual-channel designs for audio and industry. Balances cost and functionality.
   • Logic: High integration, VCF/VCA friendly.
   • Models: LM13700, NE5517.
2. High Speed / Wide Bandwidth: Built for video and high-frequency sampling. Focuses on high GBP and Slew Rate.
   • Logic: Rapid response, Slew Rate > 100V/μs.
   • Models: OPA615, MAX435, LT1228.
3. Precision / Low Drift: Used in medical and precision sensors. Minimizes offset voltage and bias current.
   • Logic: Low noise and high linearity over speed.
   • Models: LT1252, CA3080.
4. Low Power / Portable: Designed for IoT and handhelds. Works at 2V-5V with microamp-level quiescent current.
   • Logic: Minimal power consumption in tiny packages.
   • Models: MAX4132, TS921.

Classification Summary Table

Category	Core Focus	Typical Applications	Key Manufacturers
General Purpose	Channel count, integrated buffers	Audio synths, AGC	TI, onsemi
High Speed	Slew Rate, GBP	Video distribution, Radar	TI, ADI
Precision	Offset voltage, linearity	Precision measurement, Medical	ADI, Renesas
Low Power	Voltage, quiescent current	Portables, IoT sensors	ST, ADI