Power indication circuit for a processor

Details Power indication circuit for a processor Power indication circuit for a processor

2002-07-12

2004-01-13

Zweizig, Jeffrey (Department: 2836)

Miscellaneous active electrical nonlinear devices, circuits, and

Signal converting, shaping, or generating

Synchronizing

Reexamination Certificate

active

06677787

ABSTRACT:

BACKGROUND
A circuit may be used to determine when a voltage signal transitions across a threshold level. For example, a microprocessor or a Very Large-Scale Integration (VLSI) circuit may need to determine when a processor voltage signal reaches an acceptable voltage level.
Traditionally, such a determination is made by a circuit that uses a stable voltage reference signal.
FIG. 1
illustrates traditional relationships
100
between a processor voltage signal, a reference voltage signal, a slightly scaled processor voltage signal, and a power indication signal at different temperatures.
Consider first a reference voltage signal
110
generated at 100° Centigrade (C). Note that the reference voltage signal
110
initially increases along with the processor voltage signal (Vcc) That is, the reference voltage signal
100
is about 400 millivolts (mV) when Vcc is 400 mV. Above that Vcc, the reference voltage signal
110
begins to stabilize. That is, the rate of increase of the reference voltage signal
110
begins to decrease (as compared to Vcc) when Vcc reaches approximately 600 millivolts (mV). Traditionally, only a limited number of stable reference voltage values can be produced by such a circuit (e.g., based on diode thresholds, silicon band gap voltages, and/or transistor thresholds associated with the circuit). In order to generate other reference voltage values, scaling circuits may be used.
A slightly scaled processor voltage signal
120
at 100° C. is generated by scaling down Vcc (e.g., with resistors). As a result, the slightly scaled processor voltage signal
120
rises at a slightly slower rate as compared to Vcc. For example, the slightly scaled processor voltage signal
120
illustrated in
FIG. 1
reaches approximately 1.0 Volt (V) when Vcc is 1.2 V.
A power indication signal
130
is then generated when the slightly scaled processor voltage signal
120
transitions past the reference voltage signal
110
. The power indication signal
130
may indicate, for example, that Vcc has now reached an acceptable voltage level for a processor. The point (e.g., the Vcc) at which the power indication signal
130
is generated is determined by the transfer curve of the circuit. This point may be modified to a desired level by, for example, adjusting the resistance used to scale down the processor voltage.
There are several disadvantages, however, with the traditional methods of generating a power indication for a processor. For example, consider a reference voltage signal
112
that is generated when the temperature of the circuit is 0° C. Note that this reference voltage signal
112
levels off at a higher value as compared to the reference voltage signal
110
at 100° C. Also note that the slightly scaled processor voltage signal
122
at 0° C. does not significantly change as compared to the signal
120
at 100° C. As a result, the power indication signal
132
is not generated until a higher Vcc is reached (e.g., the power indication signal
132
at 0° C. occurs approximately 200 mV after the power indication signal
130
at 100° C.). This temperature sensitivity is undesirable because the predetermined acceptable voltage level for the processor has not actually changed.
Moreover, because the difference between the reference voltage signal and the slightly scaled processor voltage signal is small, the circuit will be sensitive to voltage noise. For example,
FIG. 2
illustrates traditional relationships
200
between Vcc, a reference voltage signal
210
, a slightly scaled processor voltage signal
220
, and a power indication signal
230
when 200 mV of Alternating Current (AC) noise is introduced to a traditional power indication circuit. Note that the power indication signal
230
is generated multiple times because the slightly scaled processor voltage signal
220
crosses the reference voltage signal
210
many times. This result is also undesirable because no clear indication of an acceptable voltage level is provided.


REFERENCES:
patent: 4309627 (1982-01-01), Tabata
patent: 4970408 (1990-11-01), Hanke et al.
patent: 5617048 (1997-04-01), Ward et al.
patent: 6515524 (2003-02-01), Sterrantino et al.

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