LTC6401-14 Linear Technology, LTC6401-14 Datasheet - Page 11

• Manufacturer Part Number: LTC6401-14
• Description: Low Distortion Differential ADC Driver
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
only a few components as shown in Figure 6. Three
39pF capacitors and a 16nH inductor create a bandpass
fi lter with 165MHz center frequency, –3dB frequencies at
138MHz and 200MHz.
Output Common Mode Adjustment
The LTC6401-14’s output common mode voltage is set
by the V
output common mode voltage is capable of tracking V
in a range from 1V to 1.6V. Bandwidth of V
typically 14MHz, which is dominated by a low pass fi lter
connected to the V
mon mode noise generation at the outputs. The internal
common mode feedback loop has a –3dB bandwidth
around 400MHz, allowing fast rejection of any common
mode output voltage disturbance. The V
be tied to a DC bias voltage with a 0.1μF bypass capaci-
tor. When interfacing with 3V A/D converters such as the
LT22xx families, the V
V
Driving A/D Converters
The LTC6401-14 has been specifi cally designed to interface
directly with high speed A/D converters. Figure 7 shows the
CM
Figure 6. LTC6401-14 Modifi ed 165MHz for Bandpass
Filtering (Three External Capacitors, One External Inductor)
13
14
15
16
+IN
+IN
–IN
–IN
pin of the ADC.
200Ω
200Ω
OCM
IN+
IN–
pin, which is a high impedance input. The
500Ω
500Ω
OUT–
OUT+
OCM
OCM
pin and is aimed to reduce com-
12.5Ω
12.5Ω
50Ω
50Ω
LTC6401-14
pin can be connected to the
1.7pF
+OUTF
–OUTF
640114 F06
+OUT
–OUT
8
7
6
5
10Ω
10Ω
16nH
39pF
39pF
OCM
39pF
4.99Ω
4.99Ω
OCM
pin should
control is
LTC2208
OCM
LTC6401-14 with single-ended input driving the LTC2208,
which is a 16-bit, 130Msps ADC. Two external 5Ω resistors
help eliminate potential resonance associated with bond
wires of either the ADC input or the driver output. V
of the LTC6401-14 is connected to V
at 1.25V. Alternatively, an input single-ended signal can
be converted to differential signal via a balun and fed to
the input of the LTC6401-14.
Figure 8 summarizes the IMD3 performance of the whole
system as shown in Figure 7.
Figure 8. IMD3 for the Combination of LTC6401-14 and LTC2208
Figure 7. Single-Ended Input to LTC6401-14 and LTC2208
IF IN
68.5Ω
29Ω
–100
–110
–40
–50
–60
–70
–80
–90
0
0.1μF
0.1μF
SINGLE-ENDED INPUT
F
DRIVER V
S
20 40 60 80 100 120 140 160 180
= 122.8Msps
+IN
–IN
ENABLE
LTC6401-14
OUT
V
OCM
FREQUENCY (MHz)
= 2V
+OUT
–OUT
8dB GAIN
P-P
+OUTF
–OUTF
COMPOSITE
0.1μF
4.99Ω
4.99Ω
LTC6401-14
1.25V
CM
640114 F08
of the LTC2208
AIN
AIN
LTC2208 130Msps
200
–
+
LTC2208
16-Bit ADC
V
CM
640114 F07
11
640114f
OCM