LTC6400CUD-8#TRPBF Linear Technology, LTC6400CUD-8#TRPBF Datasheet - Page 11

• Manufacturer Part Number: LTC6400CUD-8#TRPBF
• Description: IC ADC DRIVER DIFF 2.2GHZ 16QFN
• Manufacturer: Linear Technology
• Type: ADC Driverr

Specifications of LTC6400CUD-8#TRPBF

• Applications: Data Acquisition
• Mounting Type: Surface Mount
• Package / Case: 16-WQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
Output Impedance Match and Filter
The LTC6400-8 can drive an ADC directly without external
output impedance matching. Alternatively, the differential
output impedance of 25Ω can be made larger, e.g. 50Ω,
by series resistors or LC network.
The internal low pass fi lter outputs at +OUTF/–OUTF
have a –3dB bandwidth of 590MHz. External capacitors
can reduce the lowpass fi lter bandwidth as shown in
Figure 5. A bandpass fi lter is easily implemented with
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.
Figure 5. LTC6400-8 Internal Filter Topology Modifi ed for Low
Filter Bandwidth (Three External Capacitors)
Figure 6. LTC6400-8 Modifi ed 165MHz for Bandpass Filtering
(Three External Capacitors, One External Inductor)
13
14
15
16
13
14
15
16
+IN
+IN
–IN
–IN
+IN
+IN
–IN
–IN
200Ω
200Ω
200Ω
200Ω
IN+
IN–
IN+
IN–
500Ω
500Ω
500Ω
500Ω
OUT–
OUT+
OUT–
OUT+
12.5Ω
12.5Ω
50Ω
50Ω
LTC6400-8
12.5Ω
12.5Ω
50Ω
50Ω
2.7pF
+OUTF
–OUTF
+OUT
–OUT
64008 F06
LTC6400-8
2.7pF
8
7
6
5
+OUTF
–OUTF
10Ω
10Ω
+OUT
–OUT
64008 F05
16nH
39pF
39pF
8
7
6
5
39pF
4.99Ω
4.99Ω
12pF
8pF
8pF
FILTERED OUTPUT
(87.5MHz)
LTC2208
Output Common Mode Adjustment
The LTC6400-8’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 LTC6400-8 has been specifi cally designed to interface
directly with high speed A/D converters. Figure 7 shows the
LTC6400-8 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 LTC6400-8 is connected to V
1.25V. Alternatively, an input single-ended signal can be
converted to differential signal via a balun and fed to the
input of the LTC6400-8.
CM
IF IN
Figure 7. Single-Ended Input to LTC6400-8 and LTC2208
pin of the ADC.
59.0Ω
27.4Ω
OCM
pin, which is a high impedance input. The
0.1μF
0.1μF
+IN
–IN
OCM
ENABLE
LTC6400-8
V
OCM
OCM
pin and is aimed to reduce com-
+OUT
–OUT
8dB GAIN
+OUTF
–OUTF
pin can be connected to the
0.1μF
4.99Ω
4.99Ω
1.25V
LTC6400-8
CM
of the LTC2208 at
OCM
AIN
AIN
LTC2208 130Msps
OCM
–
+
LTC2208
16-Bit ADC
V
pin should
CM
control is
64008 F07
11
64008f
OCM
OCM