At 02:00 PM 8/31/2003, Byron A Jeff wrote: >So here's what I know: > >1) Video needs to be buffered. >2) Video inputs needs to be terminated with 75 ohm resistors. These 2 are OK >2) Shields should be connected to Vee. NO! Vee is the substrate - needs to be connected to a negative supply voltage somewhat larger than your lowest incoming signal. For example, video is 1V p-p: sync tips are -0.3V, video is 0V through 0.7V. >Here's what I'm still confused about: > >1) Should Vee also be tied to the power supply? Yes. >2) If so should it be -5V or 0V? -5V is good - this allows you to have Vdd as high as +10V (standard cd405x). >3) Will Zoomcat's transistor buffer be sufficient? It doesn't look like a buffer, more like a switch. >4) If so then what is the relationship of the digital and analog grounds for > the transistor? Think of the 405x family as simple FET switches with a tiny bit of logic within. Vss & Vdd are the logic supply connections; Vee is the substrate. Input (and output) signals can vary between Vee and Vdd. Note that the input or output signals don't connect to or use any of the supply lines. But you have to keep the signal within the limits of Vee - Vdd. This means that you need to reference the signals to Vss. Terminating the video signals is important - it minimizes ghosting. 75R between signal and ground is standard. The 4053 looks like a resistor: 74hc405x has lower ON resistance than standard 405x family. But you are limited to plus minus 5V for Vdd and Vee respectively. The high input impedance of the buffer ensures that the ON resistance of the 405x does not reduce signal amplitude. Most standard video buffers are high speed op-amps configured as a non-inverting amplifier with a gain of 2.0 . There is a 75R resistor in series with the output of the op-amp - this is the output termination. The gain of 2 is required because of the series resistor: 1V p-p in has to be 1V p-p out at the INPUT of the next device in the chain. The output resistor forms a 2:1 voltage divider with the load's termination. In summary: connect all the video grounds together. Tie that ground to your power supply ground through a 100R resistor. Connect all the audio grounds together. Also tie that ground to your power supply ground through a 100R resistor. Power supply feeds Vee, Vss, Vdd with -5V, 0V, +5V respectively. Logic inputs swing between Vss & Vdd. Hope this helps. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 19 years of Engineering Innovation (1984 - 2003) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.