ASTM F466-79(1992)

ASTM F4bb 79 m 0759510 0512250 238 m
Designation: F 466 - 79 (Reapproved 1992)
Standard Test Method for
Small-Signal Scattering Parameters of Low-Power Transistors
in the 0.2 to 2.0-GHz Frequency Range’
This standard is issued under the fixed designation F 466; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope parameters. A capital S is used when refemng to the entire
matrix (for example, S matrix), and a lowercase s is used
1.1 This test method covers the measurement of the scat-
when referring to individual elements of the matrix (for
tering parameters of transistors operating under small-signal
example, s, I, s2,, etc.).
conditions at power levels low enough to permit continuous
3.2.1. 1 In the symbols for the individual S parameters, the
operation at safe junction temperatures without the use of
first digit of the subscript indicates the port (pair of termi-
elaborate heat sinks. It is generally applicable in the frequency
nais) at which the signal is to be read with respect to the
range between 0.2 and 2.0 GHz.
signal incident on the port indicated by the second digit. The
1.2 Procedures are given for the use of manual measuring
1 and 2 are used to designate the input and output
numbers
equipment.
S parameters that describe a
ports, respectively. The four
1.3 Mathematical transformations for converting scatter-
two-port network are defined as follows:
ing parameters to h, y, or 2 parameters are listed in Appendix
(I) The input reflection coefficient, sI,, is the complex
x1.
ratio of the signal reflected from the input terminals of the
1.4 This standard does not purport to address all of the
device under test (forward VR, C$R, (see Fig. 1)) to the signal
safety problems, if any, associated with its use. It is the
incident on the input terminals (forward V,, (see Fig. 1))
responsibility of the user of this standard to establish appro-
when the source and terminating resistances are each equal
priute safetv and health practices und determine the applica-
to the reference impedance (4 in Fig. I).
bility of regulatory limitations prior to use.
(2) The output reflection coefficient, s22, is the complex
ratio of the signal reflected from the output terminals of the
2. Referenced Document
device under test (reverse VR, C$R (see Fig. i)) to the signal
2.1 ASTM Standard:
incident on the output terminals (the applied signal, VD, 4R
E 1 Specification for ASTM Thermometers2
(see Fig. 1) is incident on the output terminals) when the
source resistance and the termination at the input of the
3. Terminology
device under test are each equal to the reference impedance
(R, in Fig. 1).
3.1 Description of Terms Specific to This Standard:
(3) The forward transmission coefficient, s21, is the com-
3.1,l scattering parameters-For linear two-port net-
of the signal transmitted through the device under
plex ratio
works terminated at input and output by the same reference
test from input to output terminals (forward VT, dT (see Fig.
impedance, scattering parameters are complex numbers that
i)) to the signal incident on the input terminals (forward V,,
describe the relative magnitude and phase of the reflected
4, (see Fig. 1)) when the source and terminating resistances
signals VR and $R (see Fig. 1) and transmitted signals VT and
are each equal to the reference impedance (& in Fig. 1).
$T (see Fig. 1) with respect to signais applied to the input and
..
(4) The reverse transmission coefficient, sI2, is the com-
output terminals of the network, V, and bD (see Fig. 1).
plex ratio of the signal transmitted through the device from
3.1.1.1 Discussion-Although the most commonly used
output to input terminals (reverse V,, @T (see Fig. 1) to the
reference impedance is 50 SI, other values may be used. The
signal incident on the output terminals (the applied signal,
reference impedance must be known to determine the input
V,, $D (see Fig. 1) is incident on the output terminals) when
and output impedances of the device under test and to
the source resistance and the termination at the input to the
convert scattering parameters by h, y, or 2 parameters.
device under test are each equal to the reference impedance
3.1.1.2 transistors-Can be considered linear networks if
(R, in Fig. 1).
measurements are made under small-signal conditions.
3.2 Symbols:
4. Summary of Test Method
3.2.1 S-The symbol S is used to designate the scattering
4.1 Scattering parameters of transistors are determined by
placing the transistor in cascade with a transmission line that
is terminated in its characteristic impedance, generally 50 Q,
1 This test method is under the jurisdiction of ASTM Committee F-1 on
Electronics, and is the direct responsibility of Subcommittee F01.i 1 on Quality
and measuring the ratios of the reflected and transmitted
and Assurance.
signals to the incident signal in both the forward and reverse
Current edition approved March 30, 1979. Published July 1979. Onginally
directions. The two reflected signals are functions of the
published as F 466 - 76 T. Last previous editon F466 - 76 T.
2 Annual Book of ASTM Standards, Vol 14.03. input and output impedances of the transistor, respectively,
AST! F4bb 79
O759510 0512251 174
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and the two transmitted signals are related to its forward and These networks shall be capable of attenuating the r-f signal
coupled to the power supply by at least 80 dB.
reverse transfer characteristics.
7.4 Directional Couplers (labeled D, R, and T in Fig. 1)
5. Significance and Use for sampling the incident, reflected, and transmitted signals,
respectively. The directivity of the directional couplers shall
5.1 This test method provides a means of characterizing
not be less than 35 dB; the reflection coeficients at terminals
transistors in a frequency range in which the measurement of
F and G shall not exceed O. 1 (-20 dB).
h, y, and 2 parameters is impractical because of the difficulty
of obtaining adequate short-circuit and open-circuit termina-
NOTE 1-The directivity of the directional couplers and the load and
tions. Scattering parameters can be used directly for circuit
source match at terminals F and G can be considered to meet the
requirements of 7.4 if the residual reflection coefficients at terminals F
design. If desired, they can be transformed mathematically to
and G do not exceed 0.023 (-32.8 dB), as specified in Annex A1.4.10.
h, y, or 2 parameters as indicated in Appendix X1.
7.5 Transistor Adapter (labeled A in Fig. i), connecting
6. Interferences
the transistor socket to the coaxial system. The reflection
6.1 The signal level applied to transistors for the measure-
coefficient caused by mismatch between the transistor
ment of small-signal parameters is very critical, especially in
adapter and terminals F and G shall not exceed 0.05 (-26
the measurement of forward characteristics. For this reason,
dB), as specified in Annex A 1.5.5. When the transistor socket
it is important not to exceed the signal level specified in
is empty, the coupling through the adapter between termi-
11.1.3. If there is doubt, the test specified in 9.4 should be
F and G shall not be greater than 0.005 (-46 dB), as
nals
applied to determine if the signal level is low enough to
specified in Annex A1.6.4.
satis@ small-signal conditions.
7.5.1 Transistor Socket providing repeatable, low-resist-
ance contact between the transistor leads and the transistor
7. Apparatus
socket within 0.5 mm of the reference plane established by
the calibration standards (see 7.7). The socket shall provide
7.1 rIf Source-Source capable of furnishing 6 to 20 mW
for the elimination of high-frequency effects caused by
of r-f power over a frequency range from 0.2 to 2.0 GHz. The
unused portions of the transistor leads.
frequency shall be accurate within f 1 % of the set value, and
7.6 Ratio- and Phase-Measuring Instruments-Instm-
the level of the predominant harmonic shall be at least 20 dB
ments capable of measuring the ratio and phase difference
below that of the fundamental.
between the signal incident on the device under test and
7.2 r-fLoad (labeled L in Fig. i), terminating the system
either the signal reflected from it or the signal transmitted
in its characteristic impedance, R,. The reflection coefficient
through it, depending on the setting of coaxial switch SI (see
of the load shall not exceed 0.005 (46 dB).
Fig. 1). When identical signals are applied to both terminals
7.3 Bias Decoupling Networks (labeled N in Fig. i),
of these instruments, the indicated ratio shall be within 2 5%
providing for the connection of bias to the device under test.
26 1
ASTM Fqbb 79 W 0759510 0512252 O00 W
4m F466
If no signal level has been agreed upon, perform the following
(0.2 dB) and the phase difference shall not exceed 0.25'.
test to determine if the test signal level is low enough to
7.7 Calibration Standards-Equipment for calibrating
the system for measurement of reflection and transmission assure linear operation of the device being measured:
parameters, consisting of the following: 9.4.1 Select the lowest frequency at which measurements
are to be made.
7.7.1 Short Circuit-A device to be inserted into the
transistor socket for providing a short-circuit termination at 9.4.2 Calibrate the system for the measurement of s21 (see
10.4).
the reference plane on which measurements are to be made.
9.4.3 Insert a typical transistor of the type to be measured
7.7.2 Through Line-A device to be inserted into the
transistor socket for connecting the input and output termi- into the test socket, apply the prescribed biases (see 12.3,
nals of the socket in a manner which preserves the character- and measure s21 (see 12.7.3).
9.4.4 Reduce the signal applied to the transistor by a
istic impedance of the system.
factor of two by inserting a coaxial, 3-dB attenuator (see
7.8 Accessories for Performance Verifcation-Equipment
7.8.1) in series with the r-f input to the system; for example,
for checking the performance of the system, consisting of the
E of Fig. 1.
following: at terminal
9.4.5 Recheck the calibration of the system.
7.8.1 Attenuator-A 3-dB fixed coaxial attenuator for
9.4.6 Remeasure transistor s21.
determining if the r-f signal level meets the requirements for
9.4.7 If the change in the magnitude of is greater than
small-signal operation of the device under test. The
1 % (0.1 dB), reduce the signal level to the device under test
attenuator shall be designed for operation in a system with
and repeat 9.4.2 through 9.4.6 until the change in s21
impedance Ro and shall be fitted with connectors that mate
magnitude caused by the 3dB reduction in signal level is less
with those used at the r-f input of the measurement system.
7.8.2 Resistive Termination (Transistor Socket)-A resis- than 1 % (0.1 dB).
tive termination to be inserted into the transistor socket for
determining the reflection coefficients at the socket. The
10. Calibration and Standardization
reflection coefficient of the termination shall not exceed
10.1 Select a circuit configuration (for example, common
0.005 (-46 dB).
base) that is compatible with the calibration standards to be
7.8.3 Short Circuit (Coaxial)-A shorî circuit for cali-
used. This may be different from the circuit configuration
brating the system at terminals F and G (see Fig. 1). The
used for transistor measurement.
device shall be fitted with a connector that mates with those
10.2 Check to see that biases are not applied to the
of the terminals (not required if 7.8.2 is available).
transistor socket.
7.8.4 Resistive Termination (Coaxial)-A resistive termi-
10.3 Calibrate for the measurement of reflection coeff-
nation for measuring the reflection coefficients at terminals
cients if both reflection and transmission coefficients are to
F and G (see Fig. 1). The reflection coefficient of the
be measured or if reflection coefficients only are to be mea-
termination shall not exceed 0.005 (-46 dB); the connector
sured. Choose for calibration the reflection coefficient that is
shall mate with those of terminals F and G (not required if
the more critical in the intended application of the transistor.
7.8.2 is available).
Adjust this reflection coeffcient to the correct response to a
7.9 Coaxial Switches (labeled S1 and S2 in Fig. i), for
short circuit (that is, unity at 180") and record the residual
connecting the ratio- and phase-measuring instruments to
values of the other S parameters. The procedure which
the reflected and transmitted signals and for facilitating the
follows in 10.3.1 through 10.3.4 should be followed when s1 I
conversion of the system for the measurement of the forward
is the more critical of the reflection parameters; if s22 is the
and reverse characteristics of the device under test.
more critical, substitute the material in brackets.
7.10 Coaxial Transmission Lines-Coaxial lines of im-
10.3.1 Adjust sI [sZ2] as follows:
pedance Ro connecting the components of the system.
10.3.1.1 Connect the system for the measurement of
7.11 Thermometer for measuring temperature in the vi-
forward [reverse] characteristics (see Fig. 1).
cinity of the transistor fixture. It shall be capable of mea--
10.3.1.2 Insert the short circuit (see 7.7.1) into the tran-
suring temperatures in the vicinity of room ambient temper-
,
sistor socket.
ature within O. 1°C (0.2'F). ASTM Precision Thermometer
10.3.1.3 Connect the ratio and phasedifference indicators
63F-62 (1 8 to 89'0 or 63C-62 (-8 to 32°C) as prescribed in
for measurement of the reflected signal.
Specification E 1 is suitable for this purpose.
10.3.1.4 Adjust the ratio and phase-difference indicators
to read 1 (O dB) and 180 deg, respectively.
8. Sampling
10.3.1.5 Record these readings as the initial values of sli
8.1 This test method determines the properties of a single
[s2J on a data sheet such as the one illustrated in Fig. 2.
specimen. If sampling procedures are used to select devices
10.3.1.6 Remove the short circuit from the transistor
for test, they must be agreed upon in advance by the parties
socket.
to the test.
10.3.2 Determine the residual val
...