TD100 delay line chip?

Allison ajp166 at bellatlantic.net
Wed Aug 31 16:45:14 CDT 2005


>
>Subject: TD100 delay line chip?
>   From: Brad Parker <brad at heeltoe.com>
>   Date: Wed, 31 Aug 2005 16:02:10 -0400
>     To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org>
>
>
>The question about the ttl oscillator jogged my memory.
>
>Anyone recognize a line of "delay line" chips with names like TD25,
>TD50, TD100, etc...  The look they were expensive at the time, like $10
>around 1976.
>
>The TD100 pinout looks like this:
>
>      +------+
>input | 1 14 | vcc
>      | 2 13 | 
>      | 3 12 | 20ns
>40ns  | 4 11 | 
>      | 5 10 | 60s
>80ns  | 6  9 | 
>gnd   | 7  8 | 100ns
>      +------+
>
>I don't have an exact part number or mfg.  (I know where I can find one
>but it's not easy and will take some work)
>
>I want to model these in verilog but I'm not exactly sure how they work.
>They are delay lines, but I'm not sure how they react.  The input seems
>to be a short pulse from high to low of about 40ns.  I'm assuming this
>produces an approx 40ns pulse after the prescibed delay, but I'm not
>entirely sure.
>
>I would love to see a few pages from a data book which describes how
>these react (enough to model them correctly).
>
>any pointers?

Treat it as if it were a transmission line with length N.  The rough length 
for wire is 1ns/ft but if the wire is wound around a grounded metallic form
the wire to ground acts like a transmission line and the insulation sets 
the spacing hence characteristic impedence as well as velocity factor.  
Allowing for velocity factor the 1ns/ft can be be more like 1.5ns/ft. So 
winding 30ft of #42 wire is actually compact and a substantial delay.

I did a DL for the 16k muxed Drams that way and found I could easily 
measure the delay and trim the timing very accurately. It was far 
more stable than RC oneshots (74121/123/9602) it was stable too.  
During testing I was using rolls of RG174 (50 ohm .125 dia coax with
a VF of .66).  Turns out that even a 100ft roll was way too long.
Bulky but easy to get 15ns (about 117.3 inches) delay accuratly.


Allison



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