Datasheet

LTC6400-26
12
640026fa
Figure 6. LTC6400-26 with 165MHz Output Bandpass Filter
Figure 7. Single-Ended Input to LTC6400-26 and LTC2208
Figure 8. IMD
3
for the Combination of LTC6400-26 and LTC2208
converted to a differential signal via a balun and fed to the
input of the LTC6400-26. Figure 8 summarizes the IMD3
performance of the whole system in Figure 7.
Test Circuits
Due to the fully-differential design of the LTC6400 and
its usefulness in applications with differing characteristic
specifi cations, two test circuits are used to generate the
information in this datasheet. Test Circuit A is DC987B,
a two-port demonstration circuit for the LTC6400 family.
The silkscreen is shown in Figure 9. This circuit includes
input and output transformers (baluns) for single-ended-
to-differential conversion and impedance transformation,
allowing direct hook-up to a 2-port network analyzer.
There are also series resistors at the output to present the
LTC6400 with a 375Ω differential load, optimizing distortion
performance. Due to the input and output transformers, the
–3dB bandwidth is reduced from 1.9GHz to 1.67GHz.
Test Circuit B uses a 4-port network analyzer to measure
S-parameters and gain/phase response. This removes the
effects of the wideband baluns and associated circuitry,
for a true picture of the >1GHz S-parameters and AC
characteristics.
APPLICATIONS INFORMATION
640026 F06
IN+ OUT–
IN– OUT+
25Ω 12.5Ω
500Ω
LTC6400-26
LTC2208
25Ω
500Ω
12.5Ω
10Ω
10Ω
4.99Ω
4.99Ω
50Ω
50Ω
13
14
15
16
7
5
6
8
39pF16nH
39pF
+OUT
+OUTF
–OUTF
–OUT
+IN
+IN
–IN
–IN
1.7pF
39pF
37.4Ω
150Ω
0.1μF
0.1μF
640026 F07
LTC6400-26
V
OCM
ENABLE
–IN
IF IN +IN
LTC2208
4.99Ω
0.1μF
LTC2208 130Msps
16-Bit ADC
1.25V
4.99Ω
26dB GAIN
+OUT
+OUTF
–OUTF
–OUT
AIN
+
AIN
–
V
CM
Figure 9. Top Silkscreen of DC987B, Test Circuit A
FREQUENCY (MHz)
0
–40
–50
–60
–70
–80
–90
–100
–110
150 250
640026 F08
50 100
200 300
SINGLE-ENDED INPUT
F
S
= 122.8Msps
DRIVER V
OUT
= 2V
P-P
COMPOSITE