Datasheet

Data Sheet AD8370
Rev. B | Page 25 of 28
APPENDIX
CHARACTERIZATION EQUIPMENT
An Agilent N4441A Balanced-Measurement System was used to
obtain the gain, phase, group delay, reverse isolation, CMRR,
and s-parameter information contained in this data sheet. With
the exception of the s-parameter information, T-attenuator pads
were used to match the 50 Ω impedance of this instrument’s ports
to the AD8370. An Agilent 4795A Spectrum Analyzer was used
to obtain nonlinear measurements IMD, IP3, and P1dB through
matching baluns and/or attenuator networks. Various other
measurements were taken with setups shown in this section.
COMPOSITE WAVEFORM ASSUMPTION
The nonlinear two-tone measurements made for this data sheet,
that is, IMD and IP3, are based on the assumption of a fixed
value composite waveform at the output, generally 1 V p-p. The
frequencies of interest dictate the use of RF test equipment, and
because this equipment is generally not designed to work in
units of volts, but rather watts and dBm, an assumption was
made to facilitate equipment setup and operation. Two sinusoidal
tones can be represented as
V
1
= V sin (2∏f
1
t)
V
2
= V sin (2∏f
2
t)
The RMS average voltage of one tone is
( )
2
11
2
0
1
=
∫
dtV
T
T
where T is the period of the waveform. The RMS average
voltage of the two-tone composite signal is
( )
1
1
2
0
1
=+
∫
dtVV
T
T
2
It can be shown that the average power of this composite
waveform is twice (3 dB) that of the single tone. This also
means that the composite peak-to-peak voltage is twice (6 dB)
that of a single tone. This principle can be used to set correct
input amplitudes from generators scaled in dBm and is correct
if the two tones are of equal amplitude and are reasonably close
in frequency.
DEFINITIONS OF SELECTED PARAMETERS
Common-mode rejection ratio (Figure 28) has been defined for
this characterization effort as
GainModeCommon
GainModealDifferenti
where the numerator is the gain into a differential load at the
output due to a differential source at the input, and the
denominator is the gain into a differential-mode load at the
output due to a common-mode source at the input. In terms of
mixed-mode s-parameters, this equates to
21
21
SDC
SDD
More information on mixed-mode s-parameters can be
obtained in a reference by Bockelman, D.E. and Eisenstadt,
W.R., Combined Differential and Common-Mode Scattering
Parameters: Theory and Simulation. IEEE Transactions on
Microwave Theory and Techniques, v 43, n 7, 1530 (July 1995).
Reverse isolation (Figure 26) is defined as SDD12.
Power supply rejection ratio (PSRR) is defined as
s
dm
A
A
where A
dm
is the differential mode forward gain (SDD21), and
A
s
is the gain from the power supply pins (VCCI and VCCO,
taken together) to the output (OPLO and OPHI, taken
differentially), corrected for impedance mismatch. The
following reference provides more information: Gray, P.R.,
Hurst, P.J., Lewis, S.H. and Meyer, R.G., Analysis and Design of
Analog Integrated Circuits, 4
th
Edition, John Wiley & Sons, Inc.,
page 422.