U.S. patent application number 11/875837 was filed with the patent office on 2008-09-25 for flexible on chip testing circuit for i/o's characterization.
This patent application is currently assigned to STMicroelectronics Pvt. Ltd.. Invention is credited to Balwant Singh, Narayanan Vijayaraghavan.
Application Number | 20080231310 11/875837 |
Document ID | / |
Family ID | 39774052 |
Filed Date | 2008-09-25 |
United States Patent
Application |
20080231310 |
Kind Code |
A1 |
Vijayaraghavan; Narayanan ;
et al. |
September 25, 2008 |
FLEXIBLE ON CHIP TESTING CIRCUIT FOR I/O'S CHARACTERIZATION
Abstract
The present invention provides a flexible on-chip testing
circuit and methodology for measuring I/O characterization of
multiple I/O structures. The testing circuit includes a register
bank, a central processing controller (CPC), a character slew
module, a delay characterization module, and a character frequency
module. The register bank stores multiple instructions, and
measurement results. The CPC fetches the instructions from the
register bank. The CPC includes various primary and secondary state
machines for interpreting the fetched instructions for execution.
Depending on the input instruction the CPC applies stimulus to the
IUT and the output of the IUT is used by the Local characterization
modules (CHARMODULE) to extract the desired characterization
parameters such as the character slew module which measures a
voltage rise/fall time either for a single voltage IUT or a
multi-voltage IUT. The Test Methodology for STIOBISC consists of an
automated ATE pattern generation from verification test benches and
automated result processing by converting the ATE data logs into
the final readable format, thereby considerably reducing the test
setup and output processing time. The testing circuit can operate
in multiple modes for selecting one of these modules.
Inventors: |
Vijayaraghavan; Narayanan;
(Delhi, IN) ; Singh; Balwant; (Uttar Pradesh,
IN) |
Correspondence
Address: |
STMicroelectronics Inc.;c/o WOLF, GREENFIELD & SACKS, P.C.
600 Atlantic Avenue
BOSTON
MA
02210-2206
US
|
Assignee: |
STMicroelectronics Pvt.
Ltd.
Greater Noida
IN
|
Family ID: |
39774052 |
Appl. No.: |
11/875837 |
Filed: |
October 20, 2007 |
Current U.S.
Class: |
324/750.3 ;
324/762.05 |
Current CPC
Class: |
G01R 31/31715
20130101 |
Class at
Publication: |
324/765 |
International
Class: |
G01R 31/26 20060101
G01R031/26 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 20, 2006 |
IN |
2312/DEL/2006 |
Claims
1. A flexible on-chip testing circuit for I/Os characterization of
a plurality of I/O structures, said I/O structures comprising one
of a multi-voltage IUT, and a single voltage IUT, said testing
circuit utilizing a plurality of operational modes for measuring
said I/Os characterization, said testing circuit comprising: a
Standard Test Interface providing a functional testing of the
plurality of I/O structures and for interfacing a STIOBISC with an
external world; a register bank module coupled to said standard
test interface for storing a plurality of instructions, and for
measuring a plurality of results; a central processing controller
(CPC) connected to said register bank module for fetching and
executing the plurality of instructions, said controller
comprising: a plurality of secondary state machines for measuring
said I/Os characterization; and a primary state machine interacting
with the plurality of secondary state machines for interpreting the
plurality of instructions; one or more characterization modules
controlled by said central processing controller and said register
bank for measuring one or more parameters.
2. The flexible on-chip testing circuit of claim 1, wherein said
Standard Test Interface comprises an IEEE1149.1 logic.
3. The flexible on-chip testing circuit of claim 1, wherein the one
or more parameters are selected from a group comprising a
propagation delay, and a voltage slew rate.
4. The flexible on-chip testing circuit of claim 1 further
comprising an analog I/O port for applying an analog voltage.
5. The flexible on-chip testing circuit of claim 1 further
comprising a test access port (TAP) for receiving and transmitting
the plurality of instructions.
6. The flexible on-chip testing circuit of claim 5, wherein said
test access port comprises one of a tap data input port (TDI), and
a tap data output port (TDO).
7. The flexible on-chip testing circuit of claim 1, wherein the one
or more characterization modules comprises a character slew module
for measuring a voltage rise time, and a voltage fall time of a
multi-voltage IUT.
8. The flexible on-chip testing circuit of claim 7, wherein said
character slew module comprising: a stepped delay generator (SDG)
receiving an input clock to generate an inverted version signal
(IUTVin), and a programmable time delayed version signal (PROBE_L),
said generator being controlled by said central processing
controller; a voltage comparator comparing a reference voltage, and
an output inversion voltage (IUTVout) to generate an output
voltage; a low to high voltage level shifter for scaling said time
delayed signal (PROBE_L) to a pad voltage (PROBE); a high to low
voltage level shifter for scaling the output voltage signal to a
core voltage signal; an inverter and a multiplexer providing a
toggle from a logic `0` to logic `1` to said output voltage, when
said output inversion voltage (IUTVout) crosses said reference
voltage; and a flip flop circuit utilizing an inverted time delayed
clock signal for sampling an output signal from said
multiplexer.
9. The flexible on-chip testing circuit of claim 1, wherein the one
or more characterization modules comprises a delay characterization
module for measuring a propagation delay of a multi-voltage input
I/O cell.
10. The flexible on-chip testing circuit of claim 9, wherein said
delay characterization module comprising: an IUT terminal for
receiving input signals from a pad; an analog cell connected to
said IUT terminal for transmitting said signals to a core, said
cell providing an EDS protection; a clipping circuit receiving an
output from said analog cell for reducing a pad voltage level to a
core voltage level, said clipping circuit utilizing a reference
voltage (Vref); a pulse generator circuit receiving an output from
said clipping circuit for generating a pulse signal corresponding
to an IUT delay; and a time to delay converter receiving said pulse
signal to convert from a pulse width time to a binary value.
11. The flexible on-chip testing circuit of claim 10, wherein said
analog cell comprises a small finite series resistance to provide a
latch-up protection for a CMOS cell.
12. A method of I/Os characterization testing for a plurality of
I/O structures through a flexible on chip testing circuit
comprising: loading a plurality of instructions into a register
bank through a standard test interface port; fetching and executing
the plurality of instructions through a central processing
controller (CPC), said instructions being stored in said register
bank; controlling a stimuli application to a plurality of IUTs
through the central processing controller; storing a plurality of
results through one or more characterization modules; shifting out
the plurality of results through the standard test interface port;
and processing the plurality of results through a custom tool to
obtain characterization results.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to chip testing circuits, and
more specifically to a flexible on-chip testing circuit for I/Os
characterization of different types of I/O structures.
[0003] 2. Discussion of the Related Art
[0004] Input/Output (I/O) buffers are features of an integrated
circuit which must be thoroughly tested because it is the I/O
element which finally interfaces the core signal to the off-chip
environment. The test of I/O circuitry involves measurement of
various I/O pin DC and AC parameters. Since fabrication
complexities have increased, hence tests have to be targeted not
only to debug design related issues but also process related ones
as considerable process spread is observed in newer technologies.
This makes it mandatory for any design to be qualified on a large
number of dies and wafers with emphasis on corner lot
characterization. Such characterization test would require a
sophisticated expensive tester and also increase test duration if
the tests are performed manually. Embedded test features for macros
such as memories have already proved to be an effective solution to
expensive testers and parametric analyzers. Although commercial
on-chip test solutions exist for other macros, most of the tests
done today for the measurement of I/O pin parameters starting from
the application of test patterns to the observation and compilation
of results are manual thus making the tests, time intensive and
prone to instrument errors. Moreover characterization tests are
performed on a few packaged dies, which do not guarantee design
robustness with process spread. Moreover not all features (such as
maximum operating frequency of an input (IUT) can be measured at
tester level.
[0005] Wafer-level tests, with their automated test programs offer
an optimal solution in reducing the test time. Another key aspect
is the time involved for debugging, when silicon results do not
adhere to the specifications. This would require a very
sophisticated tester thus enormously adding to the cost of test.
On-chip I/O test and characterization structures, which facilitate
board-level as well as wafer-level testing on a low-cost tester
with minimum test duration address all the above mentioned
challenges.
[0006] There are various parameters, which need to be analyzed for
understanding special characteristics of the I/O structures. The
parameters can be broadly classified as the DC parameters include
output voltages and currents, the input voltage threshold levels
and the pin leakage currents, whereas the Transient parameters
include propagation delay, voltage rise/fall times of output I/Os
(as they drive large off chip capacitances) and maximum frequency
of operation of the I/O circuits in input as well as output modes.
The frequency measurements can be of immense help to the core
designer, as he/she exactly knows the limiting frequencies of I/Os
for applying critical signals like clock and observing the output
values. The above parameters often become extremely significant in
a VLSI designing, like DRAM circuits, analog to digital converter
(ADC) circuits, etc.
[0007] Therefore, there is need for a novel on-chip testing
mechanism, which can provide a flexible on-chip characterization
solution for different types of I/O structures. The novel mechanism
employs an op-code based programmable test program and algorithms
with a simple and standard Test Program/Tester Setup with automatic
processing of tester results thereby resulting in an appreciable
reduction in the test time. The mechanism is a cost effective
approach for testing, and provides sufficient flexibility to
measure D/C as well as A/C characteristics.
SUMMARY OF THE INVENTION
[0008] It is an object of the present invention to provide a
flexible on-chip testing circuit for characterization of I/O pin
parameters on a plurality of I/O structures.
[0009] It is another embodiment of the present invention to provide
a circuit, which is flexible for on-chip measurement of I/O
characterizations for a multi-voltage IUT, and a single voltage
IUT.
[0010] To achieve the aforementioned objective, the present
invention provides a flexible on-chip testing circuit for I/Os
characterization of a plurality of I/O structures, said I/O
structures comprising one of a multi-voltage IUT, and a single
voltage IUT, said testing circuit utilizing a plurality of
operational modes for measuring said I/Os characterization, said
testing circuit comprising: [0011] a Standard Test Interface
providing a functional testing of the plurality of I/O structures
and for interfacing a STIOBISC with an external world; [0012] a
register bank module coupled to said standard test interface for
storing a plurality of instructions, and for measuring a plurality
of results; [0013] a central processing controller (CPC) connected
to said register bank module for fetching and executing the
plurality of instructions, said controller comprising: [0014] a
plurality of secondary state machines for measuring said I/Os
characterization; and [0015] a primary state machine interacting
with the plurality of secondary state machines for interpreting the
plurality of instructions;
[0016] one or more characterization modules controlled by said
central processing controller and said register bank for measuring
one or more parameters.
[0017] Further the present invention provides a method of I/Os
characterization testing for a plurality of I/O structures through
a flexible on chip testing circuit comprising: [0018] loading a
plurality of instructions into a register bank through a standard
test interface port; [0019] fetching and executing the plurality of
instructions through a central processing controller (CPC), said
instructions being stored in said register bank; [0020] controlling
a stimuli application to a plurality of IUTs through the central
processing controller; [0021] storing a plurality of results
through one or more characterization modules; [0022] shifting out
the plurality of results through the standard test interface port;
and [0023] processing the plurality of results through a custom
tool to obtain characterization results.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1 illustrates a test setup of a flexible on-chip
testing circuit for I/O characterization according to the present
invention.
[0025] FIG. 2 illustrates a block diagram of a flexible on-chip
testing circuit for I/O characterization according to the present
invention.
[0026] FIG. 3 illustrates a block diagram of a character slew
module for measuring a voltage rise/fall time for a multi-voltage
IUT according to the present invention.
[0027] FIG. 4 illustrates a circuit diagram of a voltage comparator
according to an embodiment of the present invention.
[0028] FIG. 5 illustrates a timing diagram for a voltage detection
mechanism according to the present invention.
[0029] FIG. 6 illustrates a block diagram for a delay
characterization module for measuring a propagation delay of a
multi-voltage input I/O cell according to the present
invention.
[0030] FIG. 7 illustrates a timing diagram of pulse generation in a
delay characterization module according to the present
invention.
[0031] FIG. 8 illustrates a schematic block diagram of a character
frequency module for measuring a maximum operating frequency and
its corresponding duty cycle in an I/O cell according to the
present invention.
[0032] FIG. 9 illustrates a flow diagram of a method for I/O's
characterization testing according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0033] The present invention provides a cost-effective and flexible
circuit and corresponding method for on-chip testing for I/O
characterizations of different types of input and output I/O
structures. The invention provides a flexible circuit for
characterizing the pin parameters of I/O structures for a
multi-voltage IUT, or a single voltage IUT.
[0034] FIG. 1 illustrates a test setup of a flexible on-chip
testing circuit for I/O characterization. A low speed and low cost
Automatic test equipment (ATE) is used for generating the patterns
required to initialize the setup for the logic inside the chip.
STIOBISC can be used for I/O characterization at wafer level as
well as package level. The `ASSEMBLER` shown is a software program
which gives an interactive and easy way to convert the patterns to
be fed inside into required bit stream. The `RESULT COMPILER` takes
the output binary data from the ATE and converts them into the
final test and characterization results, which can be directly read
by the user.
[0035] FIG. 2 illustrates a block diagram of a flexible on-chip
testing circuit for I/O characterization according to the present
invention. The testing circuit includes a Standard Test Interface
202, a Register Bank module 204, a central processing controller
(CPC) 206, and multiple characterization modules, such as 208 210
and 212. The standard test interface 102 is used to interface the
hardware from an external world. The standard test interface 202
can be any standard test interface, such as the IEEE 1149.1
standard which has been implemented in STIOBISC. The IEEE1149.1
standard also helps in testing the I/Os for functionality before
any characterization tests. Since STIOBISC is for characterizing
the I/Os, hence a couple of additional analog ports may be required
depending upon the parameter to be characterized. For this the
IEEE1149.4 standard can be considered for use as a standard test
interface.
[0036] The register bank module 204 stores a plurality of
instructions fed through the Standard Test Interface 202 and the
bank 204 also stores the results of the various measurements. The
CPC 206 is a programmable controller and consists of a number of
interconnected state machines. The main role of the CPC 206 is to
implement the flow for each testing, debugging and characterisation
command. The CPC 206 generates an operation sequence in a defined
logical manner, which is explained afterwards. Apart for generating
the sequence the CPC 206 monitors the logic for failure. If the
logic fails due to hardware fault or wrong software programming
(illegal op-codes) the CPC 206 tells the users about the failure.
The CPC 206 also interacts with outside tester handshake signals.
The algorithms on which various flows work have a very high degree
of overlapping, making hardware sharing possible. The CPC 206 is
designed in such a way that the Instruction code is easily
expandable to include other on-chip test methodologies and any
number of IUTs in future chips. The multiple characterization
modules such as 208 210 and 212 each cater to a measurement of a
particular I/O pin parameter such as a propagation delay, a voltage
slew rate, a maximum operating frequency measurement, etc.
[0037] The present invention provides a circuit and method for
on-chip testing and characterization by measuring the following I/O
pin AC parameters:
[0038] 1. Voltage rise and fall times of an input or output I/O
(with CHARMODULE1 208 being the Custom Characterization
Module).
[0039] 2. Propagation delay of an I/O in a single mode (Input or
Output) (with CHARMODULE2 210 being the Custom Characterization
Module).
[0040] 3. Maximum frequency of operation of an I/O and its
corresponding duty cycle (with CHARMODULE3 212 being the Custom
Characterization Module).
[0041] The general flow of operation of STIOBISC for the
measurement of an I/O pin parameter is as follows:
[0042] 1. Instruction corresponding to each test mode is fed in the
register bank 204 via a TAP port or a Tap Data Input (TDI).
[0043] 2. The CPC 204 interprets the instruction invokes its
corresponding internal state machines and enables the corresponding
characterization module 208.
[0044] 3. The test is run and the results are stored in the
internal registers of the register bank (206).
[0045] 4. The stored data is then shifted out of the chip via a TAP
port or a Tap Data Output (TDO).
[0046] In an embodiment of the present invention, the test circuit
has been implemented in a 90 nm CMOS technology test-chip with a
central processing controller operates according to a 9 bit
instruction code--INSTR as mentioned in Table 1, which comprises of
a 3 bit operation code as mentioned in Table 2.
TABLE-US-00001 TABLE 1 Specification of the Instruction Code
Instruction Usage INSTR[8:6] Opcode which specifies the type of
test to be run. INSTR[5] Specifies whether the delay & Voltage
Rise/Fall times measurements are to be done for Rising or falling
signal transitions. INSTR[4:0] 5 bits for selecting the IUTs for
which the timing parameters are to be measured
TABLE-US-00002 TABLE 2 Representative Set of Op-codes Binary Opcode
Value Operation FLUSH 000 Flush all contents of REGBANK and other
registers in CPC. All stored results are available in serial format
through the TDO port of TAP. PDLAY 001 Measure Propagation Delay
SLEWR 010 Measure Voltage Slew rate FREQ 011 Measure Maximum
Frequency of operation with corresponding Duty Cycle. CHARA 100
STIOBISC Self Calibration mode DEBUG 101 Self Debug Mode for
debugging failures/anomalies in the STIOBISC logic, if any.
[0047] As an embodiment of on-chip characterization measurement of
I/O pin parameters using STIOBISC, the measurement circuit and
methodology for the voltage slew rate measurement of a
multi-voltage output IUT is explained below.
[0048] FIG. 3 illustrates a block diagram of the character slew
module 208 for measuring a voltage rise/fall time for a
multi-voltage IUT according to the present invention. The
measurement methodology can be described by way of an illustration.
The rise time of a signal between 10% and 90% of a supply voltage
Vdde is to be measured. The methodology consists of a discrete time
sampling of voltage levels of an output pin of the IUT, and
comparing it with a reference voltage Vref. The reference voltage
can either be taken from an external source or through an on-chip
voltage generator (this would save an analog port). In the present
system, the `Vref` is obtained from an analog port. First the
circuit is run to detect the time (relative to a fixed start time)
at which a signal at the output pin of the IUT reaches 10% of
`Vdde`. This time is available in a binary format, which can be
shifted out through a TAP interface. The circuit is then run to
detect the time at which said output pin of the IUT reaches 90% of
Vdde. Again this time is obtained in a binary format. The
difference of these two binary values gives the rise time in binary
format. This binary value when applied to a Binary Slew to Time
Conversion (BSTC) formula gives the Rise time in nanoseconds.
[0049] The character slew module 208 primarily includes a stepped
delay generator (SDG) 302 and a voltage comparator (VSENSE) 304. In
an embodiment of the present invention, the two voltage level
shifters are not required, if the IUT is of a single-voltage type.
The SDG 302 takes a system clock (CLK) as input and generates two
clocks, one which is either a buffered or inverted version (IUTVin)
and the other which is a programmable time delayed version
(PROBE_L) with respect to the other generated clock. In the
operation of the module 208, the block 304 compares the voltage on
an output pin IUTVout of the IUT, with a reference voltage (Vref)
at a rising edge of a PROBE signal (level shifted version of
PROBE). The voltage comparator 304 is a sense-amplifier as
illustrated in FIG. 3.
[0050] The voltage comparison between the IUTVout and the Vref
takes place at the positive edge of the PROBE signal and an output
is obtained at a pin SENSEOUT of the voltage comparator 304. The
inversion of the PROBE signal is represented by PROBE_B. Therefore,
at an instance, when the PROBE signal is high and if the IUTVout is
less than the Vref then, the SENSEOUT will resolve to the supply
voltage Vdde. Otherwise it will resolve to a ground voltage
Gnd.
[0051] In another embodiment of the present invention, the
character slew module 208 is applied for measuring I/O
characterizations for a multi-voltage IUT. A sense-amplifier has to
be made with transistors and the supply voltage, which corresponds
to a pad voltage of the IUT. Therefore, a low to high voltage level
shifter LVL_LH 314 is used to convert the PROBE_L signal to a pad
voltage -PROBE and a high to low level shifter LVL_HL 306 is used
to scale the SENSEOUT to a core voltage.
[0052] The methodology involves strobing an output signal IUTVout,
across multiple cycles of the input signal at various voltage
levels during transition of the IUTVout. It is assumed that the
Rise/Fall time remains constant for a particular IUT across
multiple input cycles at a given condition of process, voltage and
temperature (PVT). Multiple cycles are given as input to the IUT
and in each cycle the output pin of IUT is strobed at a particular
voltage level and compared with the Vref. This strobing signal, the
PROBE_L, is controlled in such a manner that in each cycle the
position of the PROBE_L is shifted by a definite step value
governed by a 10 bit STEPDELAY input bus of the SDG 302. This
STEPDELAY bus is controlled by the central processing controller,
which employs a specific algorithm to increment the step
delays.
[0053] Depending whether a rise or a fall time measurement is to be
done, an inverter 308 and a multiplexer 310 is configured in such a
way that its output always toggles from logic `0` to logic `1`,
whenever the IUTVout crosses the Vref in any direction. The output
of the multiplexer 310 is then sampled by a Flip-Flop (DFF) 312,
whose clock is an inversion of the PROBE_L signal. In an embodiment
of the present invention, the flip-flop 312 is a delay (D) type
flip flop. Thus, after sampling the IUTVout signal at the positive
edge of PROBE_L, the output SENSEOUT is latched at the negative
edge of the PROBE_L. The output signal SAOUT of the flip flop
circuit 312 is then sampled by a central processing controller
(CPC) at the next positive edge of a clock and depending on the
logic value of the SAOUT, it is decided whether to increment the
STEPDELAY or not.
[0054] The Voltage Rise/Fall time measurements are critical to
output I/O buffers as they are used to drive large off chip
capacitive loads. Therefore, it is imperative that these I/Os are
checked to ascertain whether they are able to meet the requisite
Voltage Rise/Fall times for a given capacitive load. The present
system employs an on-chip circuitry to calculate the Rise/Fall time
of an output IUT. A unique measurement methodology is employed
which facilitates contact-less measurement of Voltage Rise/Fall
times. Thus the test supports reduced pin count testing which can
be done even on a low cost tester.
[0055] FIG. 4 illustrates a circuit diagram of the voltage
comparator 304 according to an embodiment of the present
invention.
[0056] FIG. 5 illustrates a timing diagram for a voltage detection
mechanism according to the present invention. The central
processing controller (CPC) 206 increments the STEPDELAY after 2
clock cycles. As a T cycle (T1, T2, etc.) with each T cycle
consisting of two clock cycles M1 and M2. During each T cycle, at
the positive edge of M1 clock, the Central controller samples for
the SAOUT signal. If the SAOUT is logic `1`, the controller stops
incrementing the STEPDELAY bits, as that would be the binary value
at which the IUTVout just crossed the Vref. If SAOUT is at logic
`0`, then the controller 206 increment the STEPDELAY bits.
[0057] During the first half of M1, the SDG 302 gets tuned to a new
value of STEPDELAY. At the negative edge of M1, a positive edge of
the PROBE_L signal is generated, which compares the IUTVout with
the Vref. The output of the comparison SENSEOUT is then latched by
the flip flop circuit 312 at the negative edge of PROBE_L which
occurs after the positive edge of M2 cycle and is available as the
SAOUT. In the diagram shown in FIG. 5, in the T cycle T4, the
IUTVout just crosses the Vref at the sampling edge of the PROBE
signal.
[0058] The delay increment between two consecutive step sizes in
the SDG 302 is an inverter delay and the range of the SDG 302 has
been kept up to 20 ns to accommodate large IUT output transitions.
Incrementing the 11 bit STEPDELAY bus serially for large
transitions, say by 15 ns (2.sup.11 T cycles), would result in a
very large test program time. Therefore, to considerably reduce the
test program time, a customized binary convergence algorithm has
been incorporated in the central controller (CPC) 206 to increment
the STEPDELAY bus. This algorithm results in the measurement of
output transitions using a maximum of 52 T cycles or
[0059] 52*2=104 clock cycles only, thus resulting in a huge
reduction in a test time.
[0060] The above mentioned procedure is then repeated with the Vref
kept at 90% of pad supply voltage. The difference of the two binary
STEPDELAY values obtained gives the rise time of the IUT from 10%
to 90% of the pad supply voltage in binary format. The voltage fall
time can also be similarly measured by just inverting the
transitions at the IUTVin pin with respect to the PROBE_L.
[0061] Before the test for IUT is done, the SDG 302 is self
calibrated and its output is used to formulate a Binary Slew to
Time Conversion (BSTC) formula which converts binary value to time
domain and thus gives the Voltage Rise/Fall in nanoseconds.
[0062] FIG. 6 illustrates a block diagram for the delay
characterization module 210 for measuring a propagation delay
according to the present invention. The delay characterization
module 210 can be used for multi-voltage I/Os (with different pad
and core voltages), and single-voltage I/Os. The module 210
utilizes a methodology, which consists of sampling the signals at
the input and output of the IUT and producing a pulse whose pulse
width is equal to the time difference between the two sampled
signals. A signal from a pad side of an IUT terminal 610 is brought
inside the chip via an analog cell 602. Each IUT has a dedicated
analog cell associated with it and the pad side pin of the analog
cell is shorted with the pad side pin of the IUT. This has been
done to propagate the pad side signal (given to the IUT 610)
directly to the core via the analog cell 602. The analog cell 602
is just a wire with a small finite series resistance (couple of K
ohms) and provides an Electrostatic Discharge (ESD) protection. The
ESD protection is required as the pad voltage is going directly to
internal blocks of the chip. Also this finite series resistance
helps to provide latch-up protection for CMOS cells taking this
signal as input.
[0063] The waveforms at points `a`, `b`, `c` and `d` are
illustrated in FIG. 7. In case of multi-voltage I/Os, the input
signal of the IUT 610, after crossing the analog cell 602, wave `a`
is fed to a voltage clipping circuit CLIPPER 604, which clips the
pad voltage Vdde to a voltage level corresponding to a core supply
Vdd. This is depicted by wave `b`. The voltage at which the input
signal should clip in the CLIPPER circuit 604 is governed by a
voltage (Vref) applied at the analog pin. The reference voltage
Vref can either be taken from an external source or through an
on-chip voltage generator (this would save an analog port). The
Propagation Delay is defined as the difference of the time when the
output reaches a certain threshold (usually 50% of supply) and the
time when the applied input reaches a certain threshold (50% of
supply). The module 210 measures a delay using 50% of supply
voltage as threshold. The output of the CLIPPER circuit 604 is now
fed to a PULSEGEN circuit 606, which produces a pulse whose width
corresponds to the delay of the IUT. This is depicted by wave`d` in
FIG. 7.
[0064] As illustrated in FIG. 7, the actual propagation delay of
the IUT is Tpd, whereas the pulse formed is equal to Tpd+Terr.
Since the input transition time at the tester is known, therefore,
Terr can be calculated mathematically from the tester slope value.
The Terr is finally subtracted from the measurement result. In case
of a falling input transition, the Terr can be similarly found and
added to the measured value. The pulse is then fed to a Time to
Digital Converter (TDC) 608 which converts the pulse width time to
binary equivalent.
[0065] Before the test for IUT is done, the TDC 608 is self
calibrated and its output is used to formulate a Binary to Time
Domain Conversion (BTDC) formula for the TDC 608 which converts
binary value obtained during delay measurement to time domain, and
thus gives the pulse width in nanoseconds.
[0066] The TDC 608 is a central block, while the CLIPPER 604 and
PULSEGEN circuits 606 are dedicated for each IUT and placed close
to it. Special measures have been taken during the place and route
to ensure that the pulse that travels from each PULSEGEN 506 to the
TDC 608 retains its pulse width with an error of 0.2%. The
individual pulses are then selected using a Selection Logic Block
(pulse is retained with an error of 0.1%) and its output is sent to
the TDC circuit 608.
[0067] FIG. 8 illustrates a schematic block diagram of the
character frequency module 212. The character frequency module 212
measures the maximum operating frequency and its corresponding duty
cycle in an input I/O cell. The character frequency module 212 is
derived from the co pending patent application number 1785/DEL/96
filed on Aug. 4, 2006.
[0068] FIG. 9 illustrates a flow diagram of a method for I/O's
characterization testing according to the present invention. The
flow chart explains the overall procedural steps for I/O's
characterization testing.
[0069] Having thus described at least one illustrative embodiment
of the invention, various alterations, modifications, and
improvements will readily occur to those skilled in the art. Such
alterations, modifications, and improvements are intended to be
within the scope of the invention. Accordingly, the foregoing
description is by way of example only and is not intended as
limiting. The invention is limited only as defined in the following
claims and the equivalents thereto.
* * * * *