Miscellaneous active electrical nonlinear devices – circuits – and – Specific input to output function
Reexamination Certificate
2001-05-17
2003-04-08
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific input to output function
C327S362000, C326S030000
Reexamination Certificate
active
06545522
ABSTRACT:
TECHNICAL FIELD
This disclosure relates generally to electronic devices, and in particular but not exclusively, relates to use of a single reference component to provide multiple circuit compensation by using digital impedance code shifting.
BACKGROUND
Because high-frequency processors are becoming more sensitive to variations in process, supply voltage, and temperature (P-V-T), it becomes prudent to compensate critical circuits for these variations. For example, on-die termination circuits, input/output (I/O) pre-driver circuits, timing control circuits, etc. are compensated because they affect overshoots, undershoots, signal reflections, timing control (Tco), and signal edge rates. Comparing a resistance of an external resistor to the resistance of an internal compensation circuit is the basis for compensating these critical circuits. Accordingly, for each kind of circuit (e.g., on-die termination circuit, I/O pre-driver circuit, Tco circuit, etc.), a separate external resistor is used to compensate each of the required circuit attributes (such as impedance, slew rate, and timing).
FIG. 1
is a schematic diagram of a circuit compensation technique that uses multiple external resistors. The technique shown in
FIG. 1
compensates a critical circuit across P-V-T by using an external resistor R (shown in
FIG. 1
as having an example value of 100 Ohms) to match a resistance of a compensation circuit
10
formed on a chip
12
. The compensation circuit
10
comprises a plurality of P-channel metal oxide semiconductor (PMOS) transistors, referred to as “transistor legs.” In the example of
FIG. 1
, there are 32 transistor legs.
Matching the on-chip internal resistance of the compensation circuit
10
to the resistance of the external resistor R is done by having a first finite state machine FSM
1
turn on the transistor legs one at a time until the effective on-chip internal resistance is approximately equal to the resistance of the external resistor R. At this moment, a comparator circuit
14
(coupled to the external resistor R, to the compensation circuit
10
, and to a voltage supply Vdd) trips, and the number of activated transistor legs in the compensation circuit
10
is recorded by the finite state machine FSM
1
.
From this number of activated transistor legs, a digital impedance code is generated by the finite state machine FSM
1
that represents the matched on-chip internal resistance. The finite state machine FSM
1
then provides this impedance code (representing 100 Ohms in the example) to other compensation circuits, such as to other Tco circuits on the chip
12
if the compensation circuit
10
compensated for timing, so that these other compensation circuits can compensate that same circuit attribute.
However, if many different circuits need to be compensated across P-V-T for different circuit attributes, a separate impedance code needs to be generated for each circuit. Thus in
FIG. 1
, n circuits to be compensated require n external resistors Rx. As is often the case, the resistance of any one of the external resistors Rx (40 Ohms as an example in
FIG. 1
) needs to be different than the resistance of the external resistor R or the resistances of other external resistors.
As apparent in
FIG. 1
, compensation of many different circuits requires many additional internal resistors (e.g., additional compensation circuits
16
), finite state machines FSMn, comparator circuits
18
, etc. The addition of these redundant on-chip components increases fabrication costs and consumes valuable real estate on the chip
12
. The use of multiple external resistors R to Rx increases packaging costs and motherboard costs, since multiple pads (e.g., pad
1
to pad n) or pins must be provided, respectively, for the external resistors R to Rx.
REFERENCES:
patent: 4628276 (1986-12-01), Mizutani
patent: 5194765 (1993-03-01), Dunlop et al.
patent: 5254883 (1993-10-01), Horowitz et al.
patent: 5844913 (1998-12-01), Hassoun et al.
patent: 6064224 (2000-05-01), Esch et al.
Lim Chee How
Mughal Usman A.
Peterson Steven A.
Uddin Razi
Blakely , Sokoloff, Taylor & Zafman LLP
Cunningham Terry D.
Intel Corporation
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