company blog about TI LMH32401IRGTR Programmable Gain Single-Ended Differential Output Transimpedance Amplifier

TI LMH32401IRGTR Programmable Gain Single-Ended Differential Output Transimpedance Amplifier

Shenzhen Mingjiada Electronics Co., Ltd. Supplies/Recycles TI LMH32401IRGTR — A high-performance programmable gain transimpedance amplifier (PGA) designed for single-ended input to differential output conversion. Specifically engineered for high-speed optical detection and signal processing applications, it leverages programmable gain, wide bandwidth, low noise, and high integration to deliver exceptional performance. Widely adopted in demanding fields such as lidar, laser ranging systems, and high-speed optical communications where signal precision and response speed are critical, it serves as an ideal front-end amplification solution for modern optoelectronic receiver systems.

I. Core Overview of the LMH32401IRGTR Device

The LMH32401IRGTR is fundamentally a single-channel transimpedance amplifier. Its core function is to convert the weak current signals generated by current-output sensors such as photodiodes into voltage signals with high speed and low distortion. Its differential output structure enhances interference resistance, while supporting programmable gain switching to adapt to applications with varying light intensities or signal amplitudes. Housed in a compact 3mm×3mm 16-pin VQFN package, the device facilitates high-density PCB layout. Its operating temperature range spans -40°C to 125°C, meeting environmental requirements for industrial-grade and select automotive-grade applications.

As a key product in TI's high-speed amplifier series, the LMH32401IRGTR prioritizes optimized high-frequency response, noise performance, and integration. It incorporates multiple practical functional modules, enabling stable operation without complex peripheral circuits. This significantly reduces system design complexity and cost while maintaining low-power control, making it suitable for portable and low-power device applications.

II. Core Technical Parameters and Performance Advantages of LMH32401IRGTR

(1) Core Technical Parameters

The LMH32401IRGTR's performance parameters revolve around three core capabilities: high speed, low noise, and programmable gain. Key specifications under typical operating conditions (VDD=3.3V, CPD=1pF, RL=100Ω, TA=25°C) precisely match real-world application requirements:

- Programmable Transimpedance Gain: Supports 2kΩ and 20kΩ gain switching with a default gain of 2kΩ. Users can flexibly configure gain via the external GAIN pin to accommodate input current signals of varying amplitudes.

- Bandwidth Performance: At 2kΩ gain, closed-loop transimpedance bandwidth reaches 450MHz; at 20kΩ gain, bandwidth is 275MHz, both delivering exceptional high-frequency response capability;

- Noise Performance: At 2kΩ gain, input reference noise is only 250nARMS; at 20kΩ gain, input reference noise drops to 49nARMS, significantly improving detection accuracy for weak signals;

- Switching Speed: At 2kΩ gain, rise/fall time is as low as 0.8ns; At 20kΩ gain, rise/fall time is 1.3ns, enabling capture of high-speed transient signals;

- Output Characteristics: Output swing reaches 1.5VPP, capable of directly driving 100Ω loads. Differential output structure supports direct connection to ADCs (analog-to-digital converters), simplifying signal chain design;

- Power Supply & Power Consumption: Single-supply operation with a voltage range of 3V to 3.45V, typical supply voltage of 3.3V, quiescent current of approximately 30mA. Supports low-power mode; can be disabled via the EN pin during idle operation to conserve power.

- Additional Parameters: Input DC current range up to 60~72μA, typical output linear drive current (sink/source) of 26.6mA, differential output impedance of approximately 21Ω, and excellent common-mode rejection ratio (CMRR).

(II) Core Performance Advantages

1. Programmable Gain for Multi-Scenario Adaptability

The LMH32401IRGTR incorporates a programmable gain control module. By configuring the GAIN pin level, it enables rapid switching between 2kΩ and 20kΩ gain settings without requiring external resistor replacement or circuit redesign. This flexibility enables adaptation to photodetection scenarios under varying light intensities: - Under strong illumination with high input current, the 2kΩ low-gain mode prevents signal saturation. - Under weak illumination with faint input signals, switching to the 20kΩ high-gain mode amplifies signal amplitude. - Low-noise performance ensures detection accuracy for faint signals remains intact.

2. High-Speed, Low-Noise Design for Optimized High-Frequency Signal Processing

The LMH32401IRGTR is specifically optimized for high-speed optoelectronic signal processing. With a maximum bandwidth of 450MHz and a fast switching speed of 0.8ns, it effortlessly captures high-frequency transient current signals in applications like lidar and high-speed optical communications without significant signal distortion. Simultaneously, its extremely low input reference noise (as low as 49 nARMS) effectively suppresses environmental noise and device-induced interference, significantly improving the signal-to-noise ratio (SNR). This resolves noise challenges during amplification of weak optoelectronic signals, making it particularly suitable for high-precision detection applications in low-light environments.

3. Single-ended Input to Differential Output Architecture with Outstanding Noise Rejection

The LMH32401IRGTR employs a single-ended input to differential output architecture. Its single-ended input directly interfaces with current-sensing devices like photodiodes, eliminating the need for additional signal conversion circuitry. The differential output effectively suppresses common-mode noise and electromagnetic interference (EMI), enhancing signal transmission stability. This makes it particularly suitable for long-distance signal transmission and applications in complex electromagnetic environments. Additionally, the differential output can directly drive the differential input port of an ADC without requiring additional differential conversion circuitry, simplifying the signal chain design while improving the ADC's sampling accuracy.

4. High Integration Reduces System Design Costs

The LMH32401IRGTR incorporates multiple practical functional modules, enabling stable operation without complex external components:

- An integrated 100mA protection clamp circuit prevents device damage from transient overcurrent or input overload while allowing rapid recovery from overload conditions, enhancing system robustness. Integrated ambient light cancellation (ALC) circuitry replaces AC-coupling capacitors between photodiodes and amplifiers, saving PCB layout space and reducing system costs. This circuit can be disabled via the IDC_EN pin to accommodate DC-coupled requirements; Integrated output multiplexing functionality enables multiple LMH32401IRGTR devices to be multiplexed to a single ADC via low-power control of the EN pin, facilitating time-division multiplexing of multi-channel signals to further reduce system cost and footprint.

5. Low-Power Control for Portable Applications

The LMH32401IRGTR supports a low-power mode. When the amplifier is not in use, the EN pin can place the device into a low-power state. During this state, the output pins enter a high-impedance condition, significantly reducing static current and effectively conserving power. This feature enables compatibility with low-power devices such as portable laser rangefinders and handheld LiDAR systems, extending device runtime. Additionally, the high-impedance output state facilitates multiplexing with multiple devices, enhancing system integration.

III. Key Functional Modules of LMH32401IRGTR

(1) Programmable Gain Control Module

The programmable gain control module is one of the core modules of the LMH32401IRGTR. The GAIN pin controls the gain switching: when the GAIN pin is pulled low, the device operates in the default 2kΩ gain mode; when the GAIN pin is pulled high, it switches to the 20kΩ gain mode. The gain switching process is fast and glitch-free, ensuring uninterrupted signal transmission and meeting signal conditioning requirements in dynamically changing light conditions. This integrated design eliminates the need for additional gain control chips or external resistor networks, simplifying circuit design while ensuring stable gain accuracy and minimizing temperature drift effects on gain.

(II) Ambient Light Cancellation (ALC) Module

The ambient light cancellation module is a specialized optimization for optoelectronic detection scenarios. It dynamically compensates for DC components generated by background ambient light (e.g., sunlight, indoor lighting), preventing amplifier output saturation caused by intense ambient light and enhancing system dynamic range. This module can directly replace the AC-coupling capacitor traditionally placed between the photodiode and amplifier, saving PCB layout space and reducing component costs. When DC-coupling is required in an application, the module can be disabled via the IDC_EN pin, offering flexible adaptation to different circuit design needs. The ALC module operates over a wide bandwidth without affecting high-frequency signal transmission, ensuring the integrity of the photoelectric signal.

(3) Protection Clamping and Low-Power Control Module

The integrated 100mA protection clamping circuit limits current amplitude during input overload, safeguarding the amplifier's input and output stages from damage. It enables rapid recovery to normal operation under overload conditions, enhancing system reliability and stability—particularly suited for applications like lidar where sudden strong signal inputs may occur. The low-power control module is managed via the EN pin. When the EN pin is pulled high, the device enters low-power mode with high-impedance output. When the EN pin is pulled low, the device operates normally. This feature not only enables power consumption control but also facilitates multi-channel signal acquisition. Through time-division control of the EN pin, multiple amplifiers can be multiplexed, reducing system hardware costs and power consumption.

(IV) Differential Output Driver Module

The differential output driver module employs a high-swing, high-speed design with an output swing of 1.5Vpp, capable of directly driving a 100Ω load without requiring additional buffer amplifiers. The module exhibits excellent common-mode rejection ratio (CMRR), effectively suppressing common-mode noise to enhance signal transmission stability. Simultaneously, the differential output directly matches the differential input of ADCs, minimizing distortion and noise interference during signal conversion to improve ADC sampling accuracy. With low output impedance and strong load-driving capability, the driver module offers high flexibility for adapting to various downstream circuit designs.

IV. LMH32401IRGTR Typical Application Circuit

The LMH32401IRGTR is typically used for amplifying optoelectronic signals in LiDAR receivers and laser rangefinders. Its typical application circuit design is straightforward, centered around a photodiode, LMH32401IRGTR, and a few peripheral components. The specific design approach is as follows:

1. Input Circuit: The photodiode's anode is grounded, while its cathode connects to the LMH32401IRGTR's IN+ pin. The IN- pin connects to a reference level (e.g., GND or a fixed bias voltage), forming a single-ended input structure. A small capacitor is connected in parallel across the photodiode to suppress high-frequency noise.

2. Gain Control: The GAIN pin connects to VDD (3.3V) or GND via a resistor to achieve fixed gain configurations of 20kΩ or 2kΩ. For dynamic gain switching, the GAIN pin can be connected to an MCU GPIO pin for software control.

3. Function Enable: The EN pin connects to an MCU GPIO pin to control the device's active/low-power mode based on system requirements. The IDC_EN pin must be pulled high to enable ambient light suppression and prevent interference from ambient light.

4. Power and Ground: VDD1 and VDD2 are both connected to a 3.3V power supply. A 0.1μF and 10μF decoupling capacitor is connected in parallel near the power pins to suppress power supply noise. The GND pin uses single-point grounding and is connected to the ground terminal of the photodiode to reduce ground loop noise.

5. Output Circuit: OUT+ and OUT- connect directly to the ADC's differential input pins. The ADC's reference voltage is configured to match the LMH32401IRGTR's VOCM pin to ensure signal compatibility. If the ADC uses single-ended input, a differential-to-single-ended conversion circuit can be used for connection.

V. LMH32401IRGTR Application Scenarios

Leveraging its high speed, low noise, programmable gain, and high integration, the LMH32401IRGTR primarily targets high-speed optoelectronic detection and signal processing applications, including:

- LiDAR: Serves as a front-end amplifier for receivers, amplifying the weak current signals from photodetectors. Suitable for automotive LiDAR and industrial LiDAR applications, enabling high-speed distance detection.

- Laser Ranging Systems: Compatible with handheld laser rangefinders and industrial laser ranging equipment, amplifying the faint photoelectric signals reflected from lasers to enhance ranging accuracy and response speed.

- High-Speed Optical Communications: Serves as a front-end amplifier for fiber optic receiver modules (ROSAs), amplifying the weak current signals from photodiodes. Suitable for high-speed optical modules, fiber optic transceivers, and similar equipment;

- Industrial Automation Photoelectric Detection: Amplifies signals for industrial sensors (e.g., photoelectric switches, photoelectric encoders), catering to high-speed, high-precision industrial inspection scenarios;

- Medical and Scientific Equipment: Compatible with PET scanners, optical coherence tomography (OCT), high-speed spectrometers, and similar devices for amplifying and conditioning weak optoelectronic signals;

- 3D Sensing and Barcode Scanning: Processes optoelectronic signals for 3D cameras and barcode scanners, improving detection accuracy and response speed.

VIII. LMH32401IRGTR Summary

The TI LMH32401IRGTR is a programmable gain transimpedance amplifier specifically designed for high-speed optoelectronic detection scenarios. Its core strengths lie in “high speed, low noise, high integration, and high flexibility.” It supports programmable gain switching between 2kΩ and 20kΩ, converts single-ended inputs to differential outputs, and incorporates practical modules such as ambient light cancellation, protection clamping, and low-power control. It achieves stable operation without complex peripheral circuits. With a maximum bandwidth of 450MHz, minimum input reference noise of 49nARMS, and fastest switching speed of 0.8ns, it perfectly suits mid-to-high-end applications like lidar, laser ranging, high-speed optical communications, and industrial photoelectric detection. Balancing cost and size advantages, it stands as the preferred front-end amplification solution for modern optoelectronic receiving systems.