Ex Parte Thiery et al

Board of Patent Appeals and Interferences

Aug 10, 2009

11264970 (B.P.A.I. Aug. 10, 2009)

UNITED STATES PATENT AND TRADEMARK OFFICE
____________________

BEFORE THE BOARD OF PATENT APPEALS
AND INTERFERENCES
____________________

Ex parte VINCENT THIERY, BRUNO NADD,
and ANDRE MOURRIER
____________________

Appeal 2009-003412
Application 11/264,9701
Technology Center 2800
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Decided: August 10, 2009
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Before MAHSHID D. SAADAT, MARC S. HOFF, and ELENI MANTIS
MERCADER, Administrative Patent Judges.

HOFF, Administrative Patent Judge.

DECISION ON APPEAL

STATEMENT OF CASE
Appellants appeal under 35 U.S.C. § 134 from a Final Rejection of
claims 1-20. We have jurisdiction under 35 U.S.C. § 6(b).
We affirm-in-part.

1 The real party in interest is International Rectifier Corporation.
Appeal 2009-003412
Application 11/264,970

Appellants’ invention relates to a driver circuit that implements a
three slope gate drive for a switch, such as a power MOSFET. The converted
drive input signal used to drive the switch has three regions: (1) a first region
in time having a first slope up to a Miller Plateau of the switch; (2) a second
region in time having a second slope that is positive, but reduced compared
with the first slope; and (3) a third region in time having a third slope greater
than the second slope. Thus, the control electrode voltage rapidly reaches the
Miller Plateau voltage, more slowly reaches a threshold voltage of the
switch, and rapidly increases once the switch has substantially fully turned
on (Spec. 3).
Claims 1 and 9 are exemplary:
1. A method of driving a power transistor switch comprising:

receiving a drive input signal;

converting the drive input signal into a converted drive input signal;
and

providing the converted gate drive input signal to a control electrode
of the switch to turn on the switch, the converted drive input signal having
three regions with respect to time, each having a slope, a first region in time
having a first slope up to a Miller Plateau of the switch; a second region in
time having a second slope with a reduced and positive slope compared with
the first slope; and a third region having a third slope that is greater than the
second slope, whereby the control electrode voltage rapidly reaches the
Miller Plateau voltage, then more slowly reaches a threshold voltage of the
switch and then, when the switch has substantially fully turned on, the
control electrode voltage is rapidly increased.

9. A method to achieve a desired delay time between the start of a drive
input signal driving a semiconductor switch and a substantially fully turned
on state of the switch, the method comprising:
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adjusting a precharge voltage on a control electrode of the switch to
maintain the desired delay time.

The Examiner relies upon the following prior art in rejecting the
claims on appeal:
Bontempo US 5,543,739 Aug. 6, 1996
Milazzo US 6,407,594 B1 Jun. 18, 2002
Tai US 2004/0145406 A1 Jul. 29, 2004
Claims 1, 2, 5-8, 11, 12, and 15-18 stand rejected under 35 U.S.C.
§ 102(b) as being anticipated by Bontempo.
Claims 1-20 stand rejected under 35 U.S.C. § 102(b) as being
anticipated by Tai.
Throughout this decision, we make reference to the Appeal Brief
(“App. Br.,” filed May 2, 2008), the Reply Brief (“Reply Br.,” filed
September 17, 2008), and the Examiner’s Answer (“Ans.,” mailed July 17,
2008) for their respective details.
ISSUES
Appellants argue that Bontempo cannot anticipate the claimed
invention because in Bontempo, the gate voltage reaches the switch’s
threshold voltage before reaching its Miller Plateau (App. Br. 5).
Appellants argue that Tai cannot anticipate the invention recited in
claims 1-8 and 11-18 because Tai contains no teaching regarding the
threshold voltage of the switch (App. Br. 8). Further, Appellants argue that
Tai does not teach a second region having a reduced (yet) positive slope
compared with the first slope, because Tai illustrates a second region with a
flat (zero) slope (App. Br. 7).
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Appellants argue that Tai does not anticipate the invention of claims
9, 10, 19, and 20 because Tai contains no discussion of adjusting a precharge
voltage, but rather confines itself to providing a desired dv/dt (App. Br. 9).
The Examiner points out that adjusting dv/dt also means adjusting the delay
associated with turning on the power transistor (Ans. 11).
The contentions of Appellants and the Examiner thus present us with
the following three issues:
1. Have Appellants shown that the Examiner erred in finding that
Bontempo teaches driving a power transistor switch, including providing a
converted gate drive input signal having the claimed regions, slopes, and
characteristics?
2. Have Appellants shown that the Examiner erred in finding that
Tai teaches driving a power transistor switch, including providing a
converted gate drive input signal having the claimed regions, slopes, and
characteristics?
3. Have Appellants shown that the Examiner erred in finding that
Tai teaches adjusting a precharge voltage on a control electrode of the
switch to maintain the desired delay time?

FINDINGS OF FACT
The following Findings of Fact (FF) are supported by a preponderance
of the evidence.
The Invention
1. According to Appellants, the invention concerns a driver circuit
that implements a three-slope gate drive for a switch, such as a power
MOSFET. The converted drive input signal used to drive the switch has
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three regions: (1) a first region in time having a first slope up to a Miller
Plateau of the switch; (2) a second region in time having a second slope that
is positive, but reduced compared with the first slope; and (3) a third region
in time having a third slope greater than the second slope. Thus, the control
electrode voltage rapidly reaches the Miller Plateau voltage, more slowly
reaches a threshold voltage of the switch, and rapidly increases once the
switch has substantially fully turned on (Spec. 3).
Bontempo
2. Bontempo teaches that in a first zone I, the gate voltage rises
from 0 V to Vth (threshold voltage) (col. 1, ll. 54-56).
3. In a second region II, the output power transistor starts to
conduct. In this saturation zone, “the gate voltage does not change much
because the contribution to the input capacitance due to the Miller effect is
preponderant” (col. 1, ll. 59-67).
Tai
4. Tai teaches that the flat middle portion of its gate voltage curve
corresponds to the Miller Plateau (Fig. 5; ¶ 0060).
5. Tai teaches current source 6 adjusting the gate voltage of the
switching element 9 to adjust a switching speed to be a desired dv/dt
(¶ 0019).

PRINCIPLES OF LAW
“A rejection for anticipation under section 102 requires that each and
every limitation of the claimed invention be disclosed in a single prior art
reference.” See In re Buszard, 504 F.3d 1364, 1366 (Fed. Cir. 2007)
(quoting In re Paulsen, 30 F.3d 1475, 1478-79 (Fed. Cir. 1994)).
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Anticipation of a claim requires a finding that the claim at issue reads on a
prior art reference. Atlas Powder Co. v. IRECO, Inc., 190 F.3d 1342, 1346
(Fed. Cir. 1999) (quoting Titanium Metals Corp. v. Banner, 778 F.2d 775,
781 (Fed. Cir. 1985)).
Under the doctrine of inherency, if a claimed element is not expressly
disclosed in a prior art reference, the reference nevertheless anticipates the
claim if the missing element is necessarily present in the reference, and it
would be so recognized by skilled artisans. Rosco, Inc. v. Mirror Lite Co.,
304 F.3d 1373, 1380 (Fed. Cir. 2002) (citations and internal quotation marks
omitted). To anticipate the claim, the missing element must be necessarily
present in the prior art—not merely probably or possibly present. Id.

ANALYSIS
SECTION 102 REJECTION OF CLAIMS 1, 2, 5-8, 11, 12, AND 15-18 OVER
BONTEMPO
Independent claims 1 and 11 recite driving a power transistor switch
with a converted drive input signal having a first region in which the control
electrode voltage rapidly reaches the Miller Plateau voltage, a second region
with a reduced but still positive slope in which the control voltage more
slowly reaches a threshold voltage of the switch, and a third region in which
the control electrode voltage slopes up more rapidly than in the second
region.
The Examiner interprets Bontempo Fig. 4, including annotations, as
teaching the converted drive input signal as claimed:
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Bontempo Figure 4, as annotated by the Examiner (Ans. 6).

Under the Examiner’s interpretation, the region from line a to line b
corresponds to the first region having a first slope up to the Miller Plateau,
and the region from line b to line d corresponds to the second region, in
which control electrode voltage slowly reaches a threshold voltage of the
switch (Ans. 7).
Figure 4 of Bontempo is identical to its Figure 2, at least with respect
to the switch turn-on portion of the curve at issue. Figure 2 features the same
horizontal dashed line that meets the gate voltage curve at the Examiner’s
line c. In Figure 2, this dashed line is marked Vth (i.e., threshold voltage).
Although the corresponding line is not marked in Figure 4, we find that,
because the figures are otherwise identical, the corresponding horizontal
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dashed line in Figure 4 also indicates the switch’s threshold voltage.
Bontempo teaches that in a first zone I, the gate voltage rises from 0 V to
Vth (threshold voltage) (FF 2). Next, in a second region II, the output power
transistor starts to conduct. In this saturation zone, “the gate voltage does
not change much because the contribution to the input capacitance due to the
Miller effect is preponderant” (FF 3).
Bontempo thus teaches that its threshold voltage is lower than its
Miller Plateau voltage, and is reached first as the gate voltage rises. As a
result of this teaching, in the Examiner’s first region (from line a to line b),
the control electrode voltage never reaches the Miller Plateau voltage,
because the Miller Plateau voltage is greater than Vth, which corresponds to
the Examiner’s line c. Further, the control electrode voltage cannot reach
the threshold voltage after it (rapidly) reaches the Miller Plateau voltage,
because Bontempo teaches that the control electrode voltage reaches the
threshold voltage first.
Bontempo therefore does not teach all of the limitations of
independent claims 1 and 11. As a result, we find error in the Examiner’s
rejection of those claims, and we will not sustain the rejection of claims 1, 2,
5-8, 11, 12, and 15-18 under 35 U.S.C. § 102(b) as anticipated by
Bontempo.
SECTION 102 REJECTION OF CLAIMS 1-8 AND 11-18 OVER TAI
As noted supra, independent claims 1 and 11 recite driving a power
transistor switch with a converted drive input signal having a first region in
which the control electrode voltage rapidly reaches the Miller Plateau
voltage, a second region with a reduced but still positive slope in which the
control voltage more slowly reaches a threshold voltage of the switch, and a
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third region in which the control electrode voltage slopes up more rapidly
than in the second region.
The Examiner, referring to Figure 5 of Tai, finds that Tai teaches the
three regions claimed.

Tai Figure 5, as annotated by the Examiner (Ans. 10).

Relying on Tai’s teaching that the flat middle portion of Tai’s Figure
5 curve corresponds to the Miller Plateau (FF 4), the Examiner finds that the
section of the graph from line b to line c corresponds to the second region
having a reduced and positive slope compared with the first slope, in which
the control electrode voltage (having reached the Miller Plateau voltage in
the first region, according to the claimed invention) more slowly reaches a
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threshold voltage of the switch. (Ans. 10). The Examiner relies on a finding
that “[i]t is inherent that threshold (sic) of a transistor is at or above the
Miller potential” to support his finding that Tai teaches the claimed
invention (Ans. 11).
We disagree with the Examiner’s finding of inherency. As discussed
supra, Bontempo provides evidence that the threshold voltage of a transistor
is not necessarily at or above the Miller potential (FF 2, 3). In the absence
of that finding of inherency, it is not necessarily true that the region of Tai’s
curve between line b and line c illustrates Tai’s gate electrode voltage more
slowly reaching the switch’s threshold voltage, because the gate electrode
voltage may have reached the threshold voltage before reaching line b on the
curve. Further, as Appellants point out, Tai does not disclose the threshold
voltage of the switch at all (App. Br. 8). Therefore, we find that Tai does
not teach a converted drive input signal having a first region with a first
slope up to a Miller Plateau of the switch, followed by a second region in
which the control electrode voltage more slowly reaches a threshold voltage
of the switch.
Because we find that Tai does not teach every element of independent
claims 1 and 11, we find error in the Examiner’s § 102 rejection of claims 1-
8 and 11-18 as being anticipated by Tai, and we will not sustain the
rejection.
CLAIMS 9, 10, 19, AND 20
We select claim 9 as representative of this group of claims, pursuant
to our authority under 37 C.F.R. § 41.37(c)(1)(vii).
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Appellants assert error in the rejection of claim 9, in that Tai does not
disclose adjusting a precharge voltage, but merely monitoring and adjusting
the gate voltage of the switch to provide a desired dv/dt (App. Br. 9).
Tai teaches current source 6 adjusting the gate voltage of the
switching element 9 to adjust a switching speed to be a desired dv/dt (FF 5).
Controlling the rate of change of gate voltage per unit time will also effect
control of the amount of time needed to charge up the gate voltage from a
starting magnitude (i.e., precharge; see Ans. 12) at which the gate voltage is
not sufficient to turn the switching element on, to a voltage magnitude at
which the switching element is turned on. This time interval corresponds to
the claim recitation of “a desired delay time between the start of a drive
input signal driving a semiconductor input switch and a substantially fully
turned on state of the switch.” Tai thus teaches means to adjust the
precharge voltage on a control electrode of a switch to maintain the desired
delay time.
Because we find that Tai teaches all of the elements of claim 9, we do
not find error in the Examiner’s rejection. Therefore, we will sustain the
rejection of claims 9, 10, 19, and 20 under 35 U.S.C. § 102 as anticipated by
Tai.
CONCLUSIONS OF LAW
1. Appellants have shown that the Examiner erred in finding that
Bontempo teaches driving a power transistor switch, including providing a
converted gate drive input signal having the claimed regions, slopes, and
characteristics.
2. Appellants have shown that the Examiner erred in finding that
Tai teaches driving a power transistor switch, including providing a
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converted gate drive input signal having the claimed regions, slopes, and
characteristics.
3. Appellants have not shown that the Examiner erred in finding
that Tai teaches adjusting a precharge voltage on a control electrode of the
switch to maintain the desired delay time.
ORDER
The Examiner’s rejections of claims 1-8 and 11-18 under 35 U.S.C.
§ 102 are reversed. The Examiner’s rejection of claims 9, 10, 19, and 20
under 35 U.S.C. § 102 is affirmed.
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No time period for taking any subsequent action in connection with
this appeal may be extended under 37 C.F.R. § 1.136(a)(1)(iv).

AFFIRMED-IN-PART

ELD

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