16-01-2016, 09:53 AM
When deciding how to wire up the input and output buses I looked at several options.
The output buses are 25swg tinned copper sleeved with some very fine silicone sleeving of which I seem to have loads. It's a bit fragile but proof against soldering irons. The output buses are each a single piece of wire, bent into a tight loop for each connection.
The input buses are 20swg tinned copper, unsleeved. They are spaced above the rest of the assembly by using a small resistor to feed each crosspoint. The value is 12R, simply because I had a load of them around. They may contribute slightly to reducing interaction when relays are switching. They will also reduce the capacitative loading on the EL2020 input buffers. Most opamps don't like capcacitative loads very much, current feedback types like the EL2020 are worse than average in this resepct. In a typical video output stage they would be driving a 75R resistor as a series termination and hence very low C.
CFB opamps are interesting. For a given process they give more bandwidth and output slew rate than voltage feedback parts. The BW is also only weakly dependent on closed loop gain and is largely set by the value of the feedback resistor. The EL2020 was the first video bandwidth opamp that was really easy to use. I think of it as the video 741. Absolute godsend to designers like me working with analogue video. I think it arrived c1989.
http://cds.linear.com/docs/en/design-note/dn46fa.pdf
The output buses are 25swg tinned copper sleeved with some very fine silicone sleeving of which I seem to have loads. It's a bit fragile but proof against soldering irons. The output buses are each a single piece of wire, bent into a tight loop for each connection.
The input buses are 20swg tinned copper, unsleeved. They are spaced above the rest of the assembly by using a small resistor to feed each crosspoint. The value is 12R, simply because I had a load of them around. They may contribute slightly to reducing interaction when relays are switching. They will also reduce the capacitative loading on the EL2020 input buffers. Most opamps don't like capcacitative loads very much, current feedback types like the EL2020 are worse than average in this resepct. In a typical video output stage they would be driving a 75R resistor as a series termination and hence very low C.
CFB opamps are interesting. For a given process they give more bandwidth and output slew rate than voltage feedback parts. The BW is also only weakly dependent on closed loop gain and is largely set by the value of the feedback resistor. The EL2020 was the first video bandwidth opamp that was really easy to use. I think of it as the video 741. Absolute godsend to designers like me working with analogue video. I think it arrived c1989.
http://cds.linear.com/docs/en/design-note/dn46fa.pdf
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
