Method and Apparatus for Defining Test Sequences for a Signal Measurement System

This invention relates to electronic test instruments and, more particularly, to electronic instrumentation for signal measurements during tests performed on radio frequency (RF) and microwave systems and associated components. Specifically, the invention is directed to a method and apparatus for aiding a user to define a test sequence for configuring electronic test instruments for measuring various characteristics of RF and microwave systems and associated components being tested in response to swept frequency stimuli applied by either an internal or external signal source.

Traditionally, many signal measurement systems, such as vector network analyzers, are perceived as products for research and development engineers. However, the manufacturer is faced with finding a reasonable solution to tests on RF and microwave systems and associated components that balances low cost with performance sufficient for production test needs. There are few, if any, economy vector network analyzers designed specifically to meet the production test needs of the system or component manufacturer.

Furthermore, the need for simple control of test instruments is increasing as the test instrumentation becomes more complex. In the case of many vector network analyzers, there is an RF source, a receiver, and a display. These can be configured to make system or component measurements at different frequencies, powers, and speeds. These vector network analyzers can measure different channels with different inputs, and they can display the results in a variety of formats.

Many different attempts at simplifying repetitive measurements have been tried (ASP, that is, Auto Sequence Programming, as described in HP 4194A ASP Programming Guide, Hewlett-Packard Company Part #5920-2915 and BASIC from Anritsu Corporation and Avantest Corporation). These implementations involve a programming language and do not allow a user to control his or her instrument while setting up a measurement.

As instrumentation becomes more complex and test requirements more exhaustive, it is even more important to maintain a balance between a simple user interface and minimum test time. Complex test instruments require more user training, and the possibility of human error increases as the number of steps in the test process increases. When production volumes are high enough, many test instruments are completely automated to simplify and speed testing. However, there are many low and medium volume test applications where automation would reduce test time but does not justify the initial cost of purchasing a computer and developing custom software. Therefore, there is a need for built-in automation for manufacturing test.

One embodiment of the present invention provides a method and apparatus for facilitating definition of test sequences by a user during setup of a signal measurement system for characterizing performance of RF and microwave systems and associated components. The invention provides interactive programming of test sequences Routines are executed in real-time during entry of the steps which comprise the program sequence.

Test sequencing in accordance with the invention enables the user to automate a test without a computer and does not require any additional computer programming expertise. Operation is similar to programming a hand-held calculator. The signal measurement system simply learns the keystrokes typically used to perform a measurement, which can later be executed with the push of a single key. Each test sequence can preferably comprise as many as approximately 200 instructions. All of the test features of the signal measurement system can be automated, augmented by some basic decision-making capability (i.e., IF LIMIT TEST FAILS, DO SEQUENCE TUNE).

The preferred embodiment of the invention provides a user of the signal measurement system with softkey menus for selecting a desired test sequence, including measurement selection for the device to be tested. The signal measurement system prompts the user with a set of displayed softkey selections via a user interface to step the user through the setup process. Preferably, a signal processing unit (or analyzer) included in the signal measurement system incorporates the user interface in firmware to guide and aid the user in defining the desired test sequence. The analyzer preferably displays the softkey menus to guide the user on a cathode ray tube included in the analyzer. This facilitates proper configuration of the signal measurement system for measurements of the characteristics of devices to be tested.

One embodiment of the signal measurement system in accordance with the invention provides compact, integrated, and low cost vector network analyzer solutions for the RF and microwave frequency ranges. These vector network analyzers share a common appearance, easy-to-use operation (front panel and HP-IB) and productivity advantages.

The above and other features of the invention and the concomitant advantages will be better understood and appreciated by persons skilled in the field to which the invention pertains in view of the following description given in conjunction with the accompanying drawings. In the drawings:

FIG. 1 is a block diagram of a signal measurement system incorporating definition of test sequences by a user in accordance with one embodiment of the invention;

FIG. 2, comprising FIGS. 2A and 2B, is a flow diagram of the test sequence method for selecting a new test sequence or modifying a previous test sequence and executing the sequence in accordance with one embodiment of the invention; and

FIG. 3 illustrates a display provided by the signal measurement system shown in FIG. 1 during definition of a test sequence by the user during setup of the signal measurement system.

FIG. 1 shows an exemplary signal measurement system in the form of an RF or microwave system and associated component signal measurement system in accordance with one embodiment of the invention, generally indicated by the numeral 10. Its principal elements are a vector network analyzer 12, a source 14, shown as an external source although an internal source 14' can be incorporated, and a receiver 16. All of the elements of the signal measurement system 10, including the source 14 and the receiver 16, are extensively characterized to achieve high levels of precision in measurements. FIG. 1 also shows a device under test (DUT), for example, a mixer connected to the signal measurement system 10.

The vector network analyzer 12 preferably comprises essentially a 3 GHz vector network analyzer, for example, an HP 8753 vector network analyzer available from Hewlett-Packard Company, Network Measurements Division, Santa Rosa, Calif. It provides 300 kHz to 3 GHz or 3 MHz to 6 GHz test signals used to stimulate the DUT.

The electrical characteristics of the source 14 and the receiver 16 in a test setup have to be sensitive, stable, and repeatable. Also, their bandwidths need to be wider than that of the DUT.

The source 14 preferably provides a signal source which generates a high-stability, 1 Hz-frequency-resolution synthesized signal that can be swept from 300 kHz to 3 GHz or from 3 MHz to 6 GHz. The signal from the source 14 is then applied to the DUT.

The receiver 16 demodulates the modulated signal for processing in the vector network analyzer 12. The transmission and reflection characteristics of the DUT are then displayed, preferably on a cathode ray tube (CRT) lB included in the vector network analyzer 12, either as a function of the RF modulation frequency or as a function of RF power or distance.

The receiver 16 is a high-stability, high-resolution precision receiver with greater than 100 dB dynamic range which allows measurements over a wide dynamic range and enables the signal measurement system 10 to operate with a sensitivity of 0 dBm to -100 dBm over the 300 kHz to 3 GHz measurement range and 0 dBm to -95 dBm over the 3 GHz to 6 GHz measurement range. The receiver 16 has a dynamic accuracy over a 40 dB range of +/-0.05 dB and +/-0.3 degrees. The 3 GHz to 6 GHz bandwidths of the source 14 and the receiver 16 provide ample margin for typical tests.

The signal measurement system 10 is operable to perform various measurements. Although the present invention is not directed to these measurements per se, a general understanding of various types of measurements that can be performed will aid an understanding of the operation of enabling the user to define test sequences in accordance with the invention.

The DUT can be characterized using the signal measurement system 10. Examples of RF and microwave devices are amplifiers, filters, and cables. The RF measurements include bandwidth, insertion loss/gain, phase, group delay, and complex impedance.

Electrical measurements can be performed on such RF components as amplifiers, filters, and cables, or a complete transmitter or receiver Typical measurements include loss/gain versus modulation frequency or power level, modulation bandwidth, modulation phase shift or phase delay, distortion (e.g., group delay or deviation from linear phase), complex impedance (magnitude and phase), harmonic distortion, and electrical length (including discontinuity location).

In accordance with the invention, the signal measurement system 10 incorporates the capability for the user to define a test sequence to provide operating ease. Firmware resident in memory in the signal measurement system 10 generates displays to provide for test measurement setups which allow users unfamiliar with computer program languages to configure the signal measurement system for various types of tests. There also are menus for formatting, scaling, and plotting measurements.

In accordance with the invention, the signal processing unit (or vector network analyzer 12) included in the signal measurement system 10 incorporates in firmware a set of encoded softkey menus which allow the user to define a test sequence for a desired test on the DUT. Code for allowing definition of test sequences is embedded as a portion of the instrument mainframe firmware. Hence, the invention provides a user interface to allow the user greater ease in setting up and executing the measurement process associated with a desired test protocol.

Considered in more detail, the vector network analyzer 12 has programmed into its read only memory (ROM) firmware test sequence codes which are available to be combined to make the signal measurement system 10 easy to operate and use. These test sequence codes enable the user to set up the signal measurement system 10 test measurements easily and quickly. This feature is hereafter referred to as "test sequencing."

Test sequencing is an instrument user interface feature to assist a user in quickly and easily performing a desired test and making a measurement on the DUT. Test sequencing is implemented as a series of softkey menus which guide the user in configuring the signal measurement system 10 and setting basic instrument parameters in order to perform a specified test measurement.

The analyzer 12 displays a softkey menu when the analyzer is turned on. The user is guided through the test sequencing procedure by depressing softkeys. A set of softkey labels (softkey menu) is presented on the display of the vector network analyzer 12 by the firmware for each step in the test sequencing series. As each step of a desired test sequence is entered by the user, the step is displayed on the CRT 18. Also, the displayed steps are preferably overlaid on data measured in accordance with the test sequence.

The test sequencing procedure has various contemplated uses in a test instrument environment. There are several instances where a user might use this automation and several ways a user might develop a program.

First, a research and development environment typically finds a vector network analyzer on a bench used by one person. He or she can have a certain set of simple measurements that he or she makes often, and some more complicated ones that are needed occasionally. For the latter, the user typically uses a BASIC program language (either resident in the test instrument or on a computer) that he or she would spend a week or two to develop, debug, and ready for use. For these simple needs, access to a computer and the effort to set up a program and learn the program language, as well as the specific test instrument mnemonics, would be cost prohibitive. Test sequencing in accordance with the invention dramatically improves productivity in these circumstances, because the only knowledge required is how to use the test instrument.

In a production environment, there is sometimes a need for a complicated test or a large amount of data logging. Generally, an external computer is used for these purposes. There are also cases where high speed is needed. In these cases, a BASIC program language that can run at high speed inside a test instrument, but can be developed separately, is useful. In many production uses, however, high speed or complicated tests are not needed. Mostly, the desire is for a test that is highly repeatable (whether Monday or Friday) by a person with minimum skills. This can be solved by an external computer or by a BASIC program language test instrument, but then a person specializing in developing these programs is needed, and this is a large overhead. Test sequencing in accordance with the invention enables a technician or engineer to develop a test protocol by simply performing the measurement once. Thereafter, the production worker just needs to depress a "DO SEQUENCE" button. This is also useful for a production area that makes small quantities of components where development of specialized tests for these components would be too expensive.

When the test sequencing softkeys are depressed, the analyzer 12 enters a test sequencing mode by calling test sequencing routines stored in the ROM of the analyzer. Test sequencing enables the user to automate a test without a computer and does not require any additional programming expertise. Operation is similar to programming a hand-held calculator. The analyzer 12 simply learns the keystrokes typically used to perform a measurement, which can later be executed with the push of a single key. Each test sequence includes as many as approximately 200 instructions. All of the test features of the analyzer 12 can be automated, augmented by some basic decision-making capability (i.e., IF LIMIT TEST FAILS, DO SEQUENCE TUNE). FIG. 2 is a flow diagram of the test sequencing method in accordance with one embodiment of the invention.

The implementation of test sequencing is programmed into read only memory and uses a set of softkeys and text displayed on the display screen. The major modes of operation are: normal operation, "MODIFY SEQUENCE", and "DO SEQUENCE" modes.

During normal operation, test sequences are not used, but they can exist in memory to be run later.

The MODIFY/creation of a test sequence includes three steps:

1. turning on "MODIFY SEQUENCE"

2. performing the desired measurement

3. entering "DONE MODIFY".

The sequence is now stored and the entire measurement can be executed by pressing the sequence name.

In the modify mode, all keystrokes are recorded and shown on the display (see FIGS. 2 and 3). The name shown on the softkey function selected is used in the sequence list. These keys are added in the order entered, unless the "RPG" or "ARROW" keys are used to move forward or back through a test sequence. The user can insert a function anywhere in the test sequence simply by entering that function. A step can be deleted by using the "BACKSPACE" key. During this mode, the normal measurement display and softkeys are shown, and all functions entered behave just as without test sequencing turned on (except the "ARROW" keys, "RPG" key, and "BACKSPACE" key). To exit this mode, the user depresses the softkey "DONE MODIFY".

To enter the run mode, the user depresses the "DO SEQUENCE" softkey, and then selects the desired test sequence. The series of keystrokes entered is executed without any user intervention until the test sequence is complete.

Test sequencing also includes the ability to duplicate test sequences, delete them, print them on a printer (for documentation), title them, and store or load them from an external disc. The test sequence can also be sent to an external controller or sent to the test instrument from an external controller. A test sequence can also execute another sequence or branch to a sequence depending on the status of a limit test or loop counter. A "pseudo code" simple description of the test sequencing firmware appears below and in the flow diagram shown in FIG. 2. ##SPC1##

As shown in FIG. 2A, when the "MODIFY SEQUENCE" softkey is depressed, the test sequencing mode begins by enabling the user to select a series of steps associated with a desired measurement, as indicated by the numeral 100. The analyzer 12 inserts or deletes commands in a test sequence list, as indicated by the numeral 102. When the user completes the test sequence, he or she depresses the "DONE MODIFY" softkey, and the analyzer 12 stores the test sequence, as indicated by the numeral shown in FIG. 2A.

When the user decides to directly measure the DUT, he or she depresses the "DO SEQUENCE" softkey, as indicated by the numeral 106 shown in FIG. 2B. The analyzer 12 then performs a measurement, as indicated by the numeral 108 shown in FIG. 2B.

A simple example of a test sequence is shown below.

SEQUENCE AMPTEST

Start of Sequence

RECALL 3

HARMONIC OFF

DATA.fwdarw.MEMORY

DATA/MEM

SECOND

LIMIT TEST

ON

IF LIMIT TEST PASS THEN DO

SEQUENCE 2

IF LIMIT TEST FAIL THEN DO

SEQUENCE 3

This sequence recalls a set-up, measures 2nd harmonic in dBc, checks a test limit, and plots data if test limits are passed.

A list of the front panel commands which can be used in a test sequence appears in Appendix A. One implementation of the vector network analyzer 12 is referred to by the term "HP 8753B". The time domain option refers to the inverse Fourier transform to calculate the time domain step and impulse responses of the DUT. Furthermore, this allows the user to position a time gate over the data, which the analyzer 12 then applies directly to frequency domain data. The transform can also convert continuous wave (CW) time domain data to frequency domain for baseband analysis. A copy of the Firmware code is contained in Appendix B. ##SPC2##

Test sequencing allows any available functions to be executed automatically with a single keystroke. The test sequences can be entered from the front panel, read from an external disc, or down loaded over HP-IB from an external controller.

Test sequencing allows the user to combine a series of features, such as limit testing, harmonic measurements, and marker functions, with if/then decision capabilities into a test executable by a single keystroke. Creating a test sequence is virtually identical to making a manual measurement using the front panel. Once the user enters sequencing mode, all he or she needs to do is make the desired measurement. The analyzer 12 records the keystrokes it required to do so, storing them where they can be called up and repeated with a single keystroke. Test sequences can be stored in internal registers, or on an external disc. Test sequencing also allows the user to cascade multiple sequences to increase efficiency and reduce test times when performing longer, more elaborate tests. Furthermore, test sequencing enables the user to send HP-IB output strings to automatically control external devices, such as signal generators, power supplies, or relay actuators.

FIG. 3 illustrates a screen that is presented to the user in accordance with the invention. FIG. 3 actually depicts a test sequencing CRT display generated by the vector network analyzer 12.

The major advantage of test sequencing is based on the ease of use and the fact that the measurement and sequence construction are interactive. When the "MODIFY SEQUENCE" key is depressed, the test instrument begins to record all future keystrokes. This record is displayed on the display screen along with the actual measurement. The test instrument operates normally to perform the measurement, so the user has immediate feedback as to whether or not the test sequence is proceeding as expected. There is no need for the user to memorize the test protocol and then key it in, or to do extensive debugging after the test sequence is entered. There is no looking at reference documentation or memorizing function mnemonics, since the user is not keying in instructions. He or she is just executing normal test instrument functions. Finally, there is no real way to enter something that does not work or has a syntax problem, because the user is just using built-in test instrument functions that are all available.

The test sequencing procedure in accordance with the invention will now be compared to other known test instrument automation procedures. There are several ways to automate a test instrument. One is to have a person sit in front of it and push buttons (manual automation). Another is to have a test procedure that tells that person how to push those buttons. The other extreme is to effectively have an external computer push the buttons. Test sequencing in accordance with the invention lies between the last two approaches. This is achieved by allowing an experienced person to push buttons, and then a less experienced person can operate the test instrument as though a computer was performing the work. To accomplish this requires a form of "key sequence programming." In key sequence programming, a user executes a series of keystrokes once, and then the series can be repeated with the push of one button.

There are two known types of key sequence programming. One is on computers, such as programmable calculators, which aim for a similar end result, namely, a simple way to enter programs. The other is similar to the ASP and BASIC programming, which attempts to install a full-featured BASIC like programming language into a test instrument. Test sequencing in accordance with the invention introduces a third type which provides a middle ground.

Test sequencing does not attempt to put the full features and flexibility of a BASIC programming language into a test instrument, but it does allow a very simple way to enter a series of keystrokes. The following comparison of test sequencing to other types of key sequence programming will aid an understanding of the invention.

To help explain the differences between these approaches, several examples will be described. To compare a calculator and the signal measurement system 10, an editing and debugging cycle serves as an example. For ASP or BASIC programming versus test sequencing, a measurement will be described later.

For a calculator:

Switch to program mode. (The display changes to show a line number.)

"45.2", "ENTER". (A series of codes or alphanumerics appears in the display.)

"RECALL 02". (A code appears showing recall.)

"x". (A code appears showing multiply.)

"STORE 57". (A code appears that means something different since this is not allowed.)

"R/S". (Tell program to stop.)

Switch to run mode. (Display shows usual display.)

Now, to run the program, the user accesses the start location of the program and depresses the "R/S" key. The program runs, the result appears, and the answer is displayed, although it is not what is expected. Therefore, the user enters the program and depresses "SST" repeatedly to show each program step, and when not depressing the keys, an intermediate answer appears in the display. This helps the user find that "STORE 57" is not possible, a syntax error.

For the signal measurement system 10:

A similar example is difficult, since the signal measurement system 10 is not a general purpose calculator. But a general measurement might be:

Depress "MODIFY SEQUENCE". (A one page description of test sequencing is displayed.)

Depress the sequence name to be modified. (The normal display appears, overlaid with a sequence header.)

Depress "MEASURE A/R". ("A/R" shows on the display screen in the test sequence list, and A/R, that is, the ratio of one channel input to another, is measured on the trace.)

Depress "DATA INTO MEMORY". ("Data into Memory" appears, and the data trace is stored into memory.)

Depress "DATA/MEMORY". ("Data/Memory" appears, and the trace becomes Data/Memory.)

Depress "DONE MODIFY". (The test sequence list just entered disappears, but the display is still measuring A/R with data/memory.)

Now, run the program by depressing "DO SEQUENCE". The program runs and ends. Note that there is no syntax problem because only available functions can be entered on the signal measurement system 10, so there is no way to enter a bad line. Also, the commands appearing on the display screen are exactly the same as on the softkeys (or hard keys) depressed. There is no program language to learn. Finally, the lines are executed as entered, so even though there is no way to make a syntax error, if the user depresses something that was not intended to be pressed, the user can discern from the normal display that he or she is not measuring what was expected.

For a BASIC program:

Hit "EDIT" program key. (The normal measurement display is blanked and a line number appears.)

Key in "A/R" (or in some test instruments, hit an "A/R" key). (The command for A/R appears, for example, "measar".)

Key in "X1=D1". (This is just what appears on the display. It means put the data into some variable X.)

Key in "disp=X1*Y1/5.3". (This is what appears; it does a mathematical operation on the data in the X and Y variable arrays.)

Key in "END". (This appears on the display screen.)

Press "DONE EDIT". (The normal measurement display appears.)

Now, to run the program, the user finds the RUN program key and depresses it. Invariably, the result is "SYNTAX ERROR ON LINE 30". The user then repeats the series of commands shown above. He or she enters "EDIT", finds line 30, and retypes that line to correct it. Then he or she exits the edit mode and runs the program again.

The differences between this and test sequencing are similar to the differences described in connection with the calculator example. The user never has to leave the normal measurement display (and thus the measurement) to enter a test sequence, and the user cannot have syntax problems.

The signal measurement system 10 directly performs simple measurements on devices, including magnitude, phase, or group delay, on two channels. The user can also perform marker search and read out for maximum and minimums. Test sequencing allows any of these types of features to be strung together in a sequence.

The signal measurement system 10 incorporates an approach that allows a user to create a program as a sequence of keystrokes while performing an actual measurement. This allows someone with no knowledge or training with sequencing of test steps to be able to create and execute a test sequence. The test sequence can then be used to repeat measurements, or by an untrained user, with no concern about making mistakes.

The foregoing description is offered primarily for purposes of illustration. While a variety of embodiments has been disclosed, it will be readily apparent to those skilled in the art that numerous other modifications and variations not mentioned above can still be made without departing from the spirit and scope of the invention as claimed below.