LTC6409 Linear Technology, LTC6409 Datasheet - Page 14

• Manufacturer Part Number: LTC6409
• Description: 10GHz GBW - 1.1nV/Hz Differential Amplifier/ADC Driver
• Manufacturer: Linear Technology

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LTC6409
applicaTions inForMaTion
the input of the ADC to 50Ω can actually be detrimental
to system performance.
The definition of 3rd order intermodulation distortion
(IMD3) is shown in Figure 8. Also, a graphical repre-
sentation of how to relate IMD3 to output/input 3rd
order intercept points (OIP3/IIP3) has been depicted in
Figure 9. Based on this figure, Equation (4) gives the
definition of the intercept point, relative to the intermodu-
lation distortion.
Figure 7. LTC6409 Measured Output Noise and Noise Figure at Different Closed Loop Gains with and without Source Impedance Matching
14
OIP3 = P
O
+
V
V
V
50
50
50
IN
IN
IN
IMD3
+
–
+
–
+
–
2
1:4
1:4
1:4
100
100
100
100
600
150
150
+
–
+
–
+
–
V
V
V
OCM
OCM
OCM
150
150
200
200
500
500
1.3pF
1.3pF
0.4pF
0.4pF
1pF
1pF
e
NF = 14.41dB
e
NF = 10.43dB
e
NF = 8.81dB
no
no
no
= 4.70nV/√Hz
= 5.77nV/√Hz
= 11.69nV/√Hz
(4)
P
IMD3 is measured, as shown in Figure 9. It is calculated
in dBm as:
where R
the differential peak voltage for a single tone. Normally,
intermodulation distortion is specified for a benchmark
composite differential peak of 2V
O
P
is the output power of each of the two tones at which
O
= 10log
V
V
V
50
50
50
IN
IN
IN
L
is the differential load resistance, and V
+
–
+
–
+
–
150
150
100
100
50
50



2 • R
V
L
–
–
–
2
+
+
+
V
V
V
PDIFF
OCM
OCM
OCM
• 10
1.3pF
150
150
1.3pF
200
200
0.8pF
250
250
0.8pF
1pF
1pF
–3



6409 F07
e
NF = 17.59dB
e
NF = 16.66dB
e
NF = 13.56dB
P-P
no
no
no
= 5.88nV/√Hz
= 9.76nV/√Hz
= 14.23nV/√Hz
at the output of the
PDIFF
6409fa
(5)
is