Multi-port device analysis apparatus and method

Details Multi-port device analysis apparatus and method Multi-port device analysis apparatus and method

1998-11-30

2002-02-12

Beausoleil, Robert (Department: 2184)

Error detection/correction and fault detection/recovery

Data processing system error or fault handling

Reliability and availability

C712S020000, C711S100000

Reexamination Certificate

active

06347382

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a multi-port device apparatus and method for analyzing the characteristics of the multi-port device having three or more input-output terminals, and more particularly, to a multi-port device analysis apparatus and method which is capable of analyzing the multi-port device having a balanced input-output terminal or a multi-port device having different input-output impedance by using a conventional unbalanced two port type network analyzer and a conventional unbalanced multi-port test set having three or more ports.
BACKGROUND OF THE INVENTION
In order to analyze the characteristics of the communication devices or communication components used in various communication systems, a network analyzer is frequently used. A network analyzer obtains the data of various test parameters, such as a transfer function, reflection characteristics or a group delay of a high frequency components (device under test) used in a communication system by observing the frequency response of the high frequency components resulted in response to a sweep frequency signal.
A network analyzer is usually comprised of two ports, one input port and one output port. The input port sends a sweep frequency signal (test signal) to the device under test and the output port receives the response output signal of the device under test. The input port and the output port of the network analyzer are usually organized such that either port can be switched to the other by a switching operation. An example of schematic structure of such a network analyzer is shown in the block diagram of FIG.
1
.
The configuration and operation of the network analyzer which is shown in
FIG. 1
is briefly explained. A network analyzer
10
has two input-output ports P
1
and P
2
which are connected to bridges (or directional couplers)
11
and
12
, respectively. Each of the bridges
11
and
12
functions as a signal separation circuit. A test signal from a signal generator
15
is sent to one of either the bridge
11
or bridge
12
which is selected by a switch
13
. The test signal is sent from the selected one of the port P
1
or port P
2
to the device under test. The test signal from the signal generator
15
is also sent to the inside of the network analyzer as a reference signal. Namely, this reference signal and the input signal from the bridge are respectively provided to frequency converters
17
,
18
and
19
whereby converted to signals of lower frequencies. The frequency converted input signal and the reference signal are respectively converted to digital signals by corresponding AD converter
21
,
22
and
23
. These digital signals are processed by a digital signal processor (DSP)
25
to obtain those data such as transfer functions, scattering parameters, and group delays. The data showing these characteristics are displayed by a display
29
in various formats under the control of a CPU
28
which controls the overall operation of the system.
The devices to be tested, which are components such as used in the communication systems, are sometimes formed with not only two terminals but also three or four terminals (hereinafter may be referred to as “multi-port device” if necessary). In order to analyze the characteristic of the multi-port devices by using the network analyzer comprising two ports, the measurement can be performed by terminating either one of the terminals of the device
30
to be tested by the characteristic impedance as shown in FIG.
2
A. However, since this configuration causes various problems, the configuration using a multi-port test set as shown
FIG. 2B
is employed. The multi-port test set is provided between the two port network analyzer and the multi-port device to perform the characteristic analysis of the multi-port device accurately as well as easily. The connections of the components among the multi-port test set
20
, the network analyzer
10
and the multi-port device
30
are shown in FIG.
2
B. In this example, the multi-port test set
20
includes four input-output ports Q
1
-Q
4
.
In the network analyzer or the multi-port test set in a high frequency band as described above, each of the ports is in an unbalanced form and the input-output impedance is fixed to 50 ohm (or 75 ohm). Also, in the past, most of the conventional devices to be tested are configured in the unbalanced form with the impedance of 50 ohm. However, owing to the recent development of the semiconductor technology as well as the advancement and complication in the communication system, some of the recent multi-port devices to be tested employ the configurations which are different from that of conventional devices to be tested. An example of a basic structure of such a multi-port device
40
is shown in the circuit diagram of FIG.
3
. In this example, an input terminal T
1
is an unbalanced type and its impedance is 50 ohm while between output terminals T
2
and T
3
is formed of a balanced type with an impedance of 150 ohm.
Under the conventional technology, the testing of the balanced type multi-port device having a relatively high impedance as described above by using an unbalanced type network analyzer or a multi-port test set having a low impedance is performed according to the configuration as shown in FIG.
4
. Namely, a balance-unbalance converter
42
is connected to the device
40
to be tested thereby converting a balanced output of the device to be tested to an unbalanced output. The input terminals T
4
and T
5
of the converter
42
are a balanced type and have 150 ohm impedance therebetween, and are connected to the output terminals T
2
and T
3
of the device
40
to be tested, respectively. The output terminal T
6
of the converter
42
is formed as an unbalanced type and has an impedance of 50 ohm. Accordingly, the characteristic of the device to be tested is obtained by connecting the input terminal T
1
and the output terminal T
6
to the network analyzer.
According to the conventional measuring method using this converter, the measured value of the device under test
40
alone cannot be obtained because the measured result includes the characteristics of the balance-unbalance converter
42
. In addition, owing to the use of the converter
42
, even though the characteristic of the input terminal T
1
and the output terminal T
6
and the characteristic between these two terminals can be measured, the characteristic of other terminals cannot be obtained. For example, the characteristic of the balanced output terminals of the device under test cannot be obtained. In addition, because the balance-unbalance converter
42
needs to have the function to convert the output impedance of the device to be tested into the impedance of the multi-port test set
20
or the Network analyzer
10
, it is necessary to prepare various kinds of converters in accordance with the impedance value of the devices to be tested.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a multi-port device analysis apparatus and method which is capable of accurately measuring a multi-port device under test having an input-output terminal structure or an impedance different from that of the conventional devices to be tested.
It is another object of the present invention is to provide a multi-port device analysis apparatus and method which is capable of measuring a multi-port device having a balanced output ports without using a balance-unbalance converter.
It is a further object of the present invention is to provide a multi-port device analysis apparatus and method which is capable of measuring a multi-port device having a balanced port by using a multi-port test set or network analyzer having unbalanced input-output ports.
It is a further object of the present invention is to provide a multi-port device analysis apparatus and method which is capable of measuring a multi-port device having a impedance different from the impedances of the multi-port test set or net work analyzer by using such a multi-port test set and a network analyzer.
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