Duane,
I don't know TBR 21 at all, but the last modem I worked on -
(20 months ago, V.34) the British Standard BS 6305 was in effect,
which as I recall was Non-linear. To the best of my knowledge,
NET 4 = BS 6305. A Darlington is the way to go in that case.
And you can go out the back-top of their graph (see it, and know
what I mean).
Sorry, but I don't know what TBR may or may not have superceded
this since.
Best regards,
Stephen C. Phillips
Telecom Engineer
===============================================
Direct: 508-244-8116 Fax: 508-244-8039
| | Cisco Systems, Inc.
||| ||| Core Business Unit
||||| ||||| 250 Apollo Drive
||||||||| ||||||||| Chelmsford, MA 01824
||||||||||||||||||||||||| U.S.A.
E-mail: [email protected]
===============================================
NOTE: CHANGE OF ADDRESS.
All opinions expressed are my own, not necessarily those of Cisco Systems.
----- Begin Included Message -----
>From [email protected] Fri Aug 23 23:39:09 1996
To: [email protected]
Subject: UK Holding Circuit
Hello TREG'rs,
I'm having difficulty designing a UK holding circuit on a PC card.
The difficulty is caused by two I-V templates. One is from NET 4
and the other from TBR 21. The holding circuit for each template
is different.
The template from NET 4, 4.5 DC characteristics (Figure 1) has soft
current limiting, linearly dropping from 60 mA at 40V to 125 mA at 0V.
The TBR 21 template Figure 4: (TE voltage/current characteristics)
has 60 mA brick wall current limiting. It drops straight down from
36.2V to 0V.
To meet NET 4 template causes the holding circuit darlington
transistor to generate a large amount of heat. I don't think a PC
card will not survive long under those conditions.
I have a design using FET's which works well, but using FET's is
not possible. I know from past experience a FET holding circuit
cannot be used in a V.34 design. They kill V.34 receiver performance in a
certain percent of manufactured modems (About 12%).
Does anyone know which template is the correct one to use?
Thank you in advance.
Regards,
Duane Marcroft
Telecom Consultant
----- End Included Message -----
