AD8331_15 Datasheet, PDF (20/56 Pages) Analog Devices – Ultralow Noise VGAs with Preamplifier and Programmable R

AD8331/AD8332/AD8334
TEST CIRCUITS
MEASUREMENT CONSIDERATIONS
Figure 55 through Figure 68 show typical measurement
configurations and proper interface values for measurements
with 50 Ω conditions.
Short-circuit input noise measurements are made as shown in
Figure 62. The input-referred noise level is determined by
dividing the output noise by the numerical gain between Point A
and Point B and accounting for the noise floor of the spectrum
analyzer. The gain should be measured at each frequency of
interest and with low signal levels because a 50 Ω load is driven
directly. The generator is removed when noise measurements
are made.
NETWORK ANALYZER
OUT ^50Ω
50Ω _IN
18nF _270Ω
0.1µF _237Ω
FB*
120nH
0.1µF
INH
DUT
28Ω
1:1
22pF
0.1µF _237Ω
0.1µF
28Ω
*FERRITE BEAD
LMD
Figure 55. Test Circuit—Gain and Bandwidth Measurements
NETWORK ANALYZER
OUT ^50Ω
50Ω _IN
18nF 10kΩ
0.1µF _237Ω
FB*
10kΩ _120nH 0.1µF _INH
DUT
28Ω
1:1
22pF
0.1µF _237Ω
LMD
28Ω
*FERRITE BEAD
0.1µF
VGN
Figure 56. Test Circuit—Frequency Response for Various Matched Source Impedances
NETWORK ANALYZER
OUT ^50Ω
50Ω _IN
0.1µF _237Ω
FB*
120nH ^0.1µF _INH
DUT
28Ω
1:1
22pF
0.1µF _237Ω
LMD
*FERRITE BEAD
28Ω
0.1µF
VGN
Figure 57. Test Circuit—Frequency Response for Unterminated LNA, RS = 50 Ω
Rev. G | Page 20 of 56