Advertisement

Article

World’s first video signal conditioners with AGC and back-porch clamp-to-ground

Sunnyvale, CA Maxim Integrated Products introduces the MAX7450/ MAX7451/ MAX7452 family of complete front-end, standard-definition video signal conditioners. Each device restores the DC level of the AC-coupled video input, corrects for amplitude variations up to 6dB, detects fault conditions, and filters out-of-band noise. These devices optimize the video input-signal quality for further video processing through a crosspoint switch or a video decoder. They compensate for cable loss or initial amplitude variations from various video sources.

The MAX7450/MAX7451/MAX7452 are ideal in security and other video-switching applications where the camera input connects to the video switch matrix.
This family of video signal conditioners operates from ±5V (MAX7450), ±3V (MAX7451), and +5V (MAX7452).

The MAX7450/ MAX7451 set the output blanking level of the video signal to GND using a back-porch clamp approach. The MAX7452 features a user-adjustable back- porch clamp level ranging from 1V to 1.5V.

Each device integrates an input video clamp, automatic gain control (AGC), loss-of-sync detector, and an out-of-band lowpass filter (fc = 10MHz). An external pin adjusts the output buffer gain between +6dB or 0dB to drive either a 150-ohm video load with a full 2Vp-p video signal or a 1Vp-p video signal. These devices also feature an AGC disable function.

www.maxim-ic.com

Maxim is pretty excited about this product. The company says it's the first video signal conditioner with automatic gain control. Maxim has a right to be excited because this will see a good fit in the booming security market. Security applications can use this because it will resolve problems they have with camera-to-monitor quality. For example, a security camera with 1,000 feet of cable running to the switch matrix typically loses amplitude over that distance as a result of cable loss and/or noise. In applications that have many switch matrices, the brightness on all the outputs ends up being dissimilar because the video signal is different at each output.

The MAX7450 et al have the unique capability to make all the signals uniform. They do this by fixing the amplitude variations in the signal and thus make it a signal you can use. Of course, this is not the only design method to accomplish a uniform signal. You can do the same thing by using a programmable gain amplifier, sync separator, a couple switches, and some op amps, but at a cost of about $20.

How does Maxim make this work with just one chip? It takes an AC-coupled input and has a DC-restore clamp where the DC value is set for the AC-coupled input signal. On a split supply part it is controlled to ground using a clamp on the output. It has a ±6dB AGC, so for a video signal ranging from 0.5Vpp to 2Vpp it will look at the sync-clamp and fix the amplitude of the signal accordingly to have either a 1Vpp or 2Vpp output. It also has a buffer gain setting. That means if you want to drive something like a 150-ohm video load or a high-impedance load you can change the buffer setting. This is TTL logic and can be changed on the fly, which makes it very useful.

The Maxim video conditioners use an 8-pin SOIC that costs just a couple dollars, a significant improvement from the design-your-own cost of about $20. This will be a big hit for the security market since that has become a prominent issue in recent years in just about every nook and cranny of the world. There are hundreds of small companies and several large companies that will find this to be a very interesting and worthwhile product.

You might think that this could also be a wireless product, but it's currently too expensive to implement in a wireless design. Even the big security networks like the gambling casinos would not want to change from their thousands of wired cameras to a wireless design, but that could change in another 10 years. However, the bigger competitive threat to these Maxim products will come from the digital-type cameras, because security cameras are still mostly analog and the application probably will change — slowly, to digital. Unfortunately, it would be a huge investment for the large users of security cameras to switch to digital but that will change eventually.

This is an efficient solution for a specific challenge and uses a really small SOIC chip. Maxim is excited about this design, and they should be. Apparently its customers are also excited because they've been clamoring to get this product even before it was produced. That's a good problem to have.

The MAX7450/MAX7451/MAX7452 are low-cost, high-performance replacements for standard discrete components and op-amp-based AGC circuits. They are available in a tiny 8-pin SO package and operate in the extended temperature range (-40°C to +85°C). Prices start at $1.49 (1000-up, FOB USA).

7450 data sheet

0 comments on “World’s first video signal conditioners with AGC and back-porch clamp-to-ground

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.