Testing frequency hopping devices

Details Testing frequency hopping devices Testing frequency hopping devices

2000-06-30

2003-05-13

Moise, Emmanuel L. (Department: 2133)

Error detection/correction and fault detection/recovery

Pulse or data error handling

Digital logic testing

C714S724000, C455S067700, C370S252000, C375S132000, C375S138000, C343S703000

Reexamination Certificate

active

06564350

ABSTRACT:

This invention relates generally to automatic test equipment, and more particularly to using automatic test equipment to test RF and microwave devices that rapidly switch between different operating frequencies.
BACKGROUND OF THE INVENTION
Manufacturers of RF and microwave integrated circuits frequently use automatic test equipment (ATE) to verify newly manufactured devices. Testing devices early in the manufacturing process generally reduces manufacturing costs. Therefore, manufacturers preferably test integrated circuits prior to packaging the devices or attaching leads.
Oftentimes, manufacturers categorize integrated circuits based upon tested performance. The more accurately ATE systems can test integrated circuits, the more accurately manufacturers can grade devices across different levels of performance. As manufacturers generally receive higher prices for better-performing chips, accurate testing often leads to increased profits.
FIG. 1
is a simplified illustration of a conventional ATE configuration for testing RF and microwave integrated circuits. As shown in
FIG. 1
, an RF DUT (device under test)
132
is connected to a test system
100
, such as the Catalyst™ test system from Teradyne, Inc., of Boston, Mass. The DUT
132
receives an RF input signal V
3
and generates an RF output signal V
4
. The DUT
132
also receives signals for communicating with the test system
100
via digital I/O
122
.
The input signal V
3
of the DUT
132
includes a modulation signal V
1
and a high frequency carrier signal V
2
. The modulation signal V
1
generally includes a separate, low frequency carrier signal in addition to low frequency modulation components. A signal source, such as an arbitrary waveform generator (AWG)
128
, produces the modulation signal V
1
. An RF source, such as a high-frequency synthesizer
118
, produces the high frequency carrier signal V
2
. A mixer
124
combines the modulation signal V
1
and the high frequency carrier signal V
2
to produce the DUT input signal V
3
. Owing to the operation of the mixer
124
, the input signal V
3
to the DUT
132
includes frequency components that correspond to the sum and difference of the frequency components that constitute the signals V
1
and V
2
. Optionally, a low pass filter is provided at the output of the mixer
124
, to filter the components that correspond to the difference in frequencies of the signals V
1
and V
2
.
In response to the input signal V
3
, the DUT
132
generates an output signal V
4
. . . . To measure the output signal V
4
, the automatic test system
100
employs a second high-frequency synthesizer
120
and a second mixer
126
. The second mixer
126
combines the output signal V
4
with the output of the second synthesizer
120
(V
5
) to produce a test signal V
6
. The test signal V
6
includes frequency components that correspond to the sum and difference of the frequencies of the signals V
4
and V
5
. A low pass filter (not shown) is generally provided at the output of the second mixer
126
to filter the frequency components that correspond to the sum of the frequencies of the signals V
4
and V
5
A high-speed digitizer
130
measures the frequency components that correspond to the difference of the signals by sampling the signal test V
6
. Operating on the sampled data, the test system
100
performs one or more digital signal processing (DSP) algorithms to characterize the DUT
132
. These algorithms may include a test for phase noise of the DUT
132
.
To test phase noise, the test system
100
performs a Fast Fourier Transform (FFT) on the samples acquired from the high-speed digitizer
130
. Noise components are identified in the resulting power spectrum, and the level of each noise component is measured. The levels of the noise components are then compared with one or more predetermined thresholds. The DUT generally passes the test if the noise levels are below the threshold(s). Otherwise, the DUT generally fails the test.
As shown in
FIG. 1
, the test system
100
also includes a high-speed digital subsystem
116
(HSD). The HSD
116
receives instructions from the host computer
110
via a computer bus
134
. In response to these instructions, the HSD generates accurately timed commands. The HSD
116
conveys these commands, via a timing bus
136
, to the Digital I/O
122
, the AWG
128
, and the digitizer
130
. These portions of the test system
100
are constructed to rapidly respond to the commands from the HSD
116
. Therefore, the HSD
116
can accurately coordinate events that take place in these portions of the test system
200
.
Many commercial devices are available that change their carrier frequencies (i.e., “frequency hop”) at predetermined, regular intervals. For example, certain devices that conform to the “Blue Tooth” communication standard can be made to change their carrier frequency once every 625 microseconds.
We have recognized that the testing arrangement of
FIG. 1
cannot accurately measure the characteristics of these Blue Tooth devices as they frequency hop at their specified rate. As shown in
FIG. 1
, the synthesizers
118
and
120
of
FIG. 1
are programmed by a host computer
110
. We have recognized commands from the host computer
110
suffer from timing irregularities, which manifest themselves in timing irregularities in programming the synthesizers. We have found that these irregularities are significant and unpredictable.
The timing irregularities of commands from the host computer
110
generally preclude ATE systems from accurately testing Blue Tooth devices as they are being frequency hopped. For certain tests, it may be possible to momentarily interrupt frequency hopping to test these devices at individual operating frequencies. It is believed, however, that doing so for all tests would negatively impact testing accuracy, because it would subject the DUT to conditions that differ significantly from the DUT's normal operating conditions.
What is needed, therefore, is a test system that is capable of testing RF and microwave devices accurately, as the devices are being frequency-hopped at their normal rates.
SUMMARY OF THE INVENTION
With the foregoing background in mind, it is an object of the invention to test frequency-hopping devices, as the operating frequencies of the devices are varied at their normal frequency-hopping rates.
It is another object of the invention to test frequency-hopping devices without being negatively impacted by the timing irregularities of commands from the host computer.
To achieve the foregoing object and other objectives and advantages, a test system for testing a device under test (DUT) includes first and second high-frequency synthesizers, a mixer, and a dynamic controller. The output of the first synthesizer is coupled to the input of the DUT. The mixer combines the output of the DUT with the output of the second synthesizer to generate a test signal, which the test system can then measure. In response to the dynamic controller, the first and second synthesizers are caused to change their output frequencies in synchronization, at tightly controlled instants in time. As the frequencies of the synthesizers are varied from frequency to frequency, the test system measures the test signal at each frequency. The test system then compares the measurements of the test signal with predetermined limits to determine whether the DUT passes or fails.
Additional objects, advantages, and novel features of the invention will become apparent from a consideration of the ensuing description and drawings.


REFERENCES:
patent: 4894829 (1990-01-01), Monie et al.
patent: 5521904 (1996-05-01), Eriksson et al.
patent: 6148020 (2000-11-01), Emi
patent: 6233437 (2001-05-01), Klenner
patent: 6236371 (2001-05-01), Beck
patent: 6275518 (2001-08-01), Takahashi et al.

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