Data processing: measuring – calibrating – or testing – Testing system – Of circuit
Reexamination Certificate
1999-11-30
2001-09-04
Shah, Kamini (Department: 2857)
Data processing: measuring, calibrating, or testing
Testing system
Of circuit
C714S736000, C714S718000, C714S712000
Reexamination Certificate
active
06285963
ABSTRACT:
BACKGROUND
The invention relates to measuring signals in a tester system.
Tester systems for testing high speed devices, such as microprocessors and microcontrollers, have increasingly become more sophisticated due to high speed requirements. Referring to
FIG. 1
, a prior art timing measurement unit (TMU)
20
is used in a tester system
8
, such as the ITS 90000GX system made by Schlumberger Technologies, Inc. A device under test (DUT)
10
is connected to a pin electronics (PE) card
12
in the tester system
8
. The PE card translates signals received in the tester system
8
into DUT logic levels and converts signals received from the DUT
10
to test system signals, such as formatted ECL wave forms. Signals from the PE card
12
are passed to pin slice electronics cards
14
, which in turn drive signals that are transmitted to corresponding high speed interface cards
16
. Each high speed interface card
16
outputs a pair of signals HSPATHA and HSPATHB to a multiplexer
18
, which selects the outputs from one of the high speed interface cards for output as signals MA and MB.
The selected pair of signals MA and MB are routed to TMU
20
, which measures the time difference between signals MA and MB, or between corresponding pairs of signals from other sources
21
(such as signals used during calibration of the tester system
8
).
Referring to
FIGS. 2 and 3
, the coarse difference between selected inputs TRIGA and TRIGB (which correspond to events to be measured, e.g., MA and MB) is measured by a coarse counter
110
. The coarse counter
110
is clocked by a divide-by-four clock CCCLK having a frequency of about 62.5 megahertz (MHz), which is buffered from a divide-by-four clock CCLK from a programmable frequency divider
116
. The coarse counter
110
starts counting on the first leading edge of CCCLK after activation of TRIGA and stops counting on the first leading edge of CCCLK after activation of TRIGB, thereby measuring the number of CCCLK clocks between TRIGA and TRIGB.
A 1 ps time measurement resolution between TRIGA and TRIGB is achieved by measuring the time difference between edges of the selected inputs TRIGA and TRIGB and the divided clock CCCLK (fine differences T
fa
and T
fb
, respectively, in
FIG. 2
) using interpolators
102
and
104
that have a resolution of 1 ps.
To control the interpolators
102
and
104
, an event error detector
100
receives signals TRIGA and TRIGB as well as divided clocks CCLK and DCLK, both running at about 62.5 MHz. The signals CCLK and DCLK from the programmable frequency divider
116
are divided down from a 312.5-MHz master clock PFDCK.
The event error detector
100
outputs signals INTERP_A (in response to activation of TRIGA) and INTERP_B (in response to activation of TRIGB), which are provided to the interpolators
102
and
104
, respectively. As shown in
FIG. 2
, the signal INTERP_A is asserted high on the rising edge of the signal TRIGA. The signal INTERP_A is maintained high until the occurrence of the second rising edge of DCLK after the leading edge of INTERP_A. The signal INTERP_B is asserted high on the rising edge of TRIGB, and INTERP_B falls low on the second rising edge of DCLK after the leading edge of INTERP_B. This guarantees that the width of the signals INTERP_A and INTERP_B are between 16 nanoseconds (ns) and 32 ns.
In response to assertion of the signals INTERP_A and INTERP_B, the two interpolators
102
and
104
generate signals AEN and BEN, respectively, for enabling fine counters
114
and
112
. Each of the fine counters
114
and
112
is clocked by ACLK, which runs at the system oscillator clock frequency of 312.5 MHz. The interpolators
102
and
104
effectively stretch the signals INTERP_A and INTERP_B by a factor of 3200 for output as fine counter enable signals AEN and BEN to achieve a fine resolution of 1 ps.
As shown in
FIG. 4A
, each interpolator includes a ramp circuit
120
and a comparator
122
for comparing the output of the ramp circuit
120
with a reference voltage. The comparator
122
outputs the enable signal AEN or BEN to the fine counter
114
or
112
.
The ramp circuit
120
includes the circuitry shown in
FIG. 4B
, which includes a first current source
142
that outputs a tiny current (e.g., 10 &mgr;A), and a second, larger current source
144
capable of producing a relatively large current (e.g., 32 mA). The large current source
144
is connected to a node of a capacitor
140
by a switch
146
, which is activated to ramp up the ramp circuit
120
in response to assertion of INTERP_A or INTERP_B. On assertion of INTERP_A(B), the large current source
144
quickly charges the capacitor
140
. When INTERP_A (B) reaches a predetermined voltage, A(B)EN is activated. The capacitor
140
continues to charge until the signal INTERP_A(B) is negated, at which time the ramp circuit
120
ramps down. The charging period is shown as period T
o
in FIG.
4
A.
During ramp down, the capacitor
140
is discharged by the tiny current source
142
at a much slower rate. The comparator
122
continues to drive the signal A(B)EN high until the capacitor
140
has discharged to a predetermined voltage, at which time the comparator
122
drives its output signal A (B) EN low. The discharge period is shown as period T
1
in FIG.
4
A.
By using a large current source of 32 mA and a tiny current source of 10 &mgr;A, the ramp circuit
120
in effect stretches the input signal INTERP_A(B) by a factor of 3200. Since the fine counter
114
or
112
runs at 312.5 MHz, the resolution achieved is 1 ps (or 1/(312.5 MHz*3200)).
Upon completion of the measurement, the contents of the fine counters
112
and
114
, clocked by ACLK, and the coarse counter
110
, clocked by the divided signal CCCLK, are retrieved by a readback logic block
118
. The time difference between events A and B, TIMEAtoB, is calculated according to Equation 1:
TIMEAtoB=(COUNTA*1 ps)
−(COUNTB*1 ps)
+(COUNTC*16 ns), Eq. (1)
where COUNTA is the value in the fine counter
114
, COUNTB is the value in the fine counter
112
, and COUNTC is the value in the coarse counter
110
.
In effect, the interpolator
102
in combination with the fine counter
114
measures the time difference between the leading edge of INTERP_A and the next leading edge of the divided clock CCCLK (on which the coarse counter
110
is activated) at 1 ps resolution. Similarly, the interpolator
104
in combination with the fine counter
112
measures the time difference between the leading edge of INTERP_B and the next leading edge of CCCLK, on which the coarse counter
110
is stopped.
SUMMARY
Among the advantages of the invention is that improved timing measurement accuracy is achieved by using an independent measurement circuit (e.g., a coarse counter and an interpolator) to measure each of the timed events. In addition, by referencing time measurements to a master clock rather than a divided clock in a tester system, the likelihood of phase errors in the time measurements is reduced.
In general, in one aspect, the invention features a tester system having a master clock, a first coarse counter clocked by the master clock and connected to stop counting upon occurrence of a first event, and a second coarse counter clocked by the master clock and connected to stop counting upon occurrence of a second event. A fine measurement circuit clocked by the master clock is configured to measure the time intervals from occurrence of the first and second events to corresponding edges of the master clock.
In general, in another aspect, the invention features a method of measuring the time interval between a first event and a second event. The number of master clocks within a capture window between the first and second events is identified. A first fine time interval is determined between a first edge of the capture window and a first edge of the master clock. A second fine time interval is determined between a second edge of the capture window and a second edge of the master clock. Then, the time interval is calculated using the number of
Fish & Richardson P.C.
Schlumberger Technologies Inc.
Shah Kamini
LandOfFree
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