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神经网络昆斯林的新闻组分类2006

Newsgroups: sci.electronics
Path: cantaloupe.srv.cs.cmu.edu!rochester!udel!gatech!asuvax!ennews!enuxha.eas.asu.edu!gsulliva
From: [e-mail] (Glenn A Sullivan)
Subject: Re: Need help with video detection circuit
Message-ID: <[e-mail]>
Summary: Build a cheap video detector
Sender: [e-mail] (USENET News System)
Organization: Arizona State University
References: <[e-mail]>
Date: Sat, 24 Apr 1993 06:37:57 GMT
Lines: 19

[e-mail] (Steve Verity) writes:
> I am trying to build a circuit that detects the presence of video (Vs.
> a blank screen) by monitoring the R,G, and B outputs of a graphics
> card.  It should be able to detect the presence of a single pixel at
> 65 MHz, which would mean detecting a 15 NS pulse.  It should also be
> able to tell the difference between a blank screen (about 300 mv)
> and a dim screen (say, around 310 mv).  Oh yes, it also needs to be
> cheap.  ............... In 
> fact the difference between completely black and completely white is
> only 650 mv.  I am wondering if I am going to have to amplify the
> video signals to make this work.  

Try a differential amplifier. Put back-to-back diodes between the collectors
restrict the voltage swing. Have 10 mA flow, with 500 ohm collector Rs, and
keep the stray C below 10 pF. Try 2N5179s. Run collector to your logic.
Allen Sullivan