NODSLEDGE – AUTOGATING DEEP DIVE

Autogating is one of the most discussed features of image intensifiers. Sometimes it’s even presented as one of the determining factors in purchasing a vision device. But what is it exactly ? How does it work ? Is there any trade-off to this feature ?
To understand autogating, it‘s important to know what a night vision image intensifier is up against: an extreme range of lighting conditions. From near total darkness or starlight-level light conditions to streetlights, muzzle flashes and, sometimes, explosions. Autogating is there to address that wide range of situations.

What Autogating Is

In non-gated, DC-powered intensifiers, like early and low-end Gen 2 (and some ANVIS Gen3) tubes, the photocathode is held at a fixed negative voltage relative to the microchannel plate (MCP) input. Light hitting the photocathode releases electrons, which are accelerated into the MCP, multiplied, and sent on to the phosphor screen to produce a visible image. The output brightness is then regulated by automatic brightness control (ABC), which lowers the MCP voltage when the scene gets too bright.

Autogating changes this paradigm by replacing the steady photocathode voltage with a rapid train of high-voltage pulses. The photocathode is only “open” (biased for electron emission) for a controlled fraction of each cycle (called duty cycle), and “closed” the rest of the time. This pulse width is varied automatically based on scene brightness, acting like an electronic shutter at kilohertz frequencies. Because the pulses are much faster than the eye can perceive, the image appears continuous, but the total electron flux is reduced and controlled in real time.

A visual demonstration of the autogating process.

How Autogating Works in Practice

An autogated power supply continuously monitors light levels, usually by sampling the current at the phosphor screen, and adjusts the way the tube operates to maintain a stable output. At very low illumination, the photocathode is left fully open so that the tube runs in a direct current state and captures every possible photon. As brightness increases, the power supply begins shortening the fraction of time the photocathode is allowed to conduct during each high-frequency cycle, effectively reducing the duty cycle and limiting the flow of electrons into the microchannel plate. In parallel, the system can also reduce the MCP voltage slightly to trim overall gain and improve handling of bright scenes.

How Autogating Differs from ABC and BSP

Automatic Brightness Control, or ABC, relies on a feedback loop that regulates output brightness by reducing the voltage applied to the microchannel plate as input light increases. This method is simple and effective, but it comes at the cost of image quality. As the MCP voltage drops, so do gain and resolution, which makes the image appear softer and with lower contrast under bright conditions. ABC is also relatively slow to react and never touches the photocathode itself, so its control over electron flow is indirect.

Two pictures taken with the same ITT F4796 tube. This is a non autogated, Gen 3 tube from the 90s. Note the softer, less contrasted image during day compared to the sharper image during night. This drop in resolution is caused by the ABC lowering the MCP voltage.

Bright Source Protection, or BSP, works very differently. Instead of constantly regulating brightness, it is designed as a safeguard against sudden, extreme illumination such as headlights or flares. When triggered, it quickly lowers photocathode voltage or even cuts off electron flow entirely to protect the MCP from damage. BSP is less about maintaining a usable picture and more about ensuring the tube survives harsh exposures. It is reactive, not proactive, and only engages when a threshold is crossed.

Autogating occupies the space between these two approaches. Unlike ABC, it is proactive and high speed, constantly adjusting the electron stream before excessive light can overwhelm the system. Unlike BSP, it is not simply a protective shutdown but a continuous regulation method that keeps the image stable across a wide range of brightness. BSP still exists in many autogated systems as a backup, but with autogating handling most of the work, it rarely needs to intervene.

The Misconception About Autogating

“Autogating is there to protect the tube from damage.” That’s something you’ve probably heard quite often if you own night vision or have been looking into it.
While it does reduce stress on the photocathode and MCP (and thus extends life), its primary function is maintaining image quality and resolution across a wide dynamic range. If all you wanted was protection, ABC and BSP would suffice, but you’d sacrifice usable imagery in bright scenes.

The real value of autogating lies in the way it transforms the operational envelope of a night vision tube. By controlling electron flow at the photocathode with high-speed gating, the system maintains useful imagery across an exceptionally wide dynamic range, from starlight to daylight. Unlike ABC, which degrades sharpness when brightness rises, autogating preserves resolution and contrast, ensuring details remain visible even around bright sources such as headlights or muzzle flashes. This not only makes the image easier to interpret but also extends the working life of the intensifier, since the photocathode and MCP are subjected to less sustained stress. Autogating also integrates seamlessly with modern hybrid systems, such as digital capture or fused night vision/thermal devices, where stable, well-controlled imagery is essential. Taken together, these benefits explain why autogating is considered a baseline feature in current-generation intensifiers rather than a luxury add-on.

So are there really tradeoffs to Autogating ?

Autogating delivers clear advantages: it stabilizes brightness, suppresses blooming, and protects the tube under challenging light conditions. But like all engineering solutions, it comes with compromises.

First, there is gating noise, the extra electronic noise that appears when the photocathode is pulsed rather than held at a steady bias. In very low light, every photon counts, and when the gate closes, the incoming signal is cut off while background noise sources remain. This lowers the signal-to-noise ratio compared to a pure DC supply, which is why some early autogated tubes looked grainier under starlight. Some designs, such as Norinco’s “ABC-3” type, tested on recent NVT-7 tubes, can run in full-DC mode at low light, eliminating gating noise entirely, then seamlessly switch into high-frequency gating as brightness rises. However, NVT’s study shows that this design currently entails a greater response lag than regular autogated power supplies.

Another trade-off is latency. Because the duty cycle is controlled by a feedback loop that samples anode current and adjusts MCP voltage, there is always a finite response time. Under sudden flashes (like headlights or muzzle fire)the tube may briefly bloom before the gate clamps down. This is not usually dangerous (bright source protection still acts as a safety net), but it can momentarily affect clarity. Photonis addressed this by developing their proprietary Ultra Fast Autogating, which drastically reduces kickoff latency.

A demonstration of Photonis’ Ultra-Fast Autogating vs standard Autogating.

Finally, autogating sometimes causes a high-pitched whine sound. This is an acoustic by-product of the high-voltage power supply. As the photocathode is pulsed at kilohertz frequencies, components such as transformers and ceramic capacitors can vibrate through the whole body, effectively turning it into a tiny speaker. The pitch often shifts with scene brightness as the duty cycle changes, and while it may be distracting to the ear, it has no impact on the image or the reliability of the tube.

These trade-offs don’t negate the value of autogating, they explain why its design is so critical. A well-implemented system maximizes the benefits while carefully managing noise, response time, and stability.

Closing Thoughts

Autogating is not a marketing gimmick, nor is it a magic “tube shield.” It is an essential evolution in image intensifier power supply design that directly improves how night vision works when confronted with the variables of real life field use. When combined with other advancements like unfilmed MCPs and halo-reduction designs, it enables the latest generation of night vision systems to handle more environments, more gracefully, than ever before.

Also, all of our complete devices are sold with autogated image intensifiers.

Sources :

Advanced Image Intensifier Night Vision System Technologies:
Status and Summary 2002

Joseph P. Estrera, Timothy Ostromek, Antonio Bacarella, Wayne Isbell,
Michael J. Iosue, Michael Saldana and Timothy Beystrum
Northrop Grumman Electro-Optical Systems, 3414 Herrmann Drive, Garland, Texas 75041

Influence of Auto-Gated Power Supply on the Performance of Image Intensifier, April 2025

LI Yaqing¹ , YANG Zhuang², GAO Tianli¹, ZHOU Shengtao¹, LI Xiaolu¹, BAO Yuanxi¹, DU Peide¹, DAI Jinghao¹, HE Jun¹, ZHANG Liyun¹, SONG Qigeng¹, WANG Guangfan¹, XU Lingji¹, ZHANG Xu¹

• 1.North Night Vision Technology Co. Ltd., Kunming 650217, China
• 2.No. 2 Military Representative Office in Kunming, Chongqing Military Representative Bureau, Kunming 650032, China