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Browse Prior Art Database

Digitally Controlled Signal Loading

IP.com Disclosure Number: IPCOM000104740D
Original Publication Date: 1993-May-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 1 page(s) / 44K

Publishing Venue

IBM

Related People

Price, WE: AUTHOR [+3]

Abstract

Disclosed is a circuit using a digitally controlled capacitor to simulate the load of a device not installed in a computer system. When the device is not installed, the capacitor is turned on to act as a load on the circuit. When the device is installed, the capacitor is turned off. Alternately, a digital capacitor with several available levels of capacitrance can be used to provide variable loading on a signal line where several optional devices may be installed by the user of a system. Since the circuit has about the same loading, whether orn ot the device is installed, it is easier to terminate while controlling signal quality and radio frequency interference (RFI).

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 79% of the total text.

Digitally Controlled Signal Loading

      Disclosed is a circuit using a digitally controlled capacitor
to simulate the load of a device not installed in a computer system.
When the device is not installed, the capacitor is turned on to act
as a load on the circuit.  When the device is installed, the
capacitor is turned off.  Alternately, a digital capacitor with
several available levels of capacitrance can be used to provide
variable loading on a signal line where several optional devices may
be installed by the user of a system.  Since the circuit has about
the same loading, whether orn ot the device is installed, it is
easier to terminate while controlling signal quality and radio
frequency interference (RFI).

      Referring to the figure, a computing device includes a driver 1
driving an output signal line 2, to which one or more optional
devices 3 may be installed by the user.  The computing device also
includes an I/O port 4.  A terminating resistor 5 is also connected
to signal line 2.  A digitally controlled capacitor 6 is connected to
vary the capacitance attached to line 2, under control of signals
from I/O port 4.  The computing device determines, by conventional
means, which I/O port 4, so that a capacitrance reflecting the
uninstalled devices is placed on line 2.

      Digitally controlled capacitor 6 may be, for example, a Hughes
HC2021 capacitor

      Alternately, an indicator line from a socket, into which an
optional device may be...