LTC6401CUD-20#PBF Linear Technology, LTC6401CUD-20#PBF Datasheet - Page 11

• Manufacturer Part Number: LTC6401CUD-20#PBF
• Description: IC ADC DRIVER DIFF 16-QFN
• Manufacturer: Linear Technology
• Type: ADC Driverr

Specifications of LTC6401CUD-20#PBF

• Applications: Data Acquisition
• Mounting Type: Surface Mount
• Package / Case: 16-WQFN Exposed Pad
• No. Of Amplifiers: 1
• Input Offset Voltage: 2mV
• Gain Db Max: 20dB
• Bandwidth: 1.3GHz
• Slew Rate: 4500V/µs
• Supply Voltage Range: 2.85V To 3.5V
• Supply Current: 50mA
• Amplifier Case Style: QFN
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
two outputs have the same gain and thus symmetrical
swing. In general, the single-ended input impedance and
termination resistor R
of R
that the single-ended input impedance is 200Ω and R
66.5Ω in order to match to a 50Ω source impedance.
The LTC6401-20 is unconditionally stable. However, the
overall differential gain is affected by both source imped-
ance and load impedance as shown in Figure 4:
The noise performance of the LTC6401-20 also depends
upon the source impedance and termination. For example,
an input 1:4 balun transformer in Figure 2 improves SNR
by adding 6dB of gain at the inputs. A trade-off between
gain and noise is obvious when constant noise fi gure
circle and constant gain circle are plotted within the same
A
S
Figure 3. Input Termination for Single-Ended 50Ω Input
Impedance
V
+
–
, R
+
–
0.1μF
1/2 R
1/2 R
V
66.5Ω
66.5Ω
=
V
50Ω
50Ω
IN
R
R
IN
G
S
S
R
R
T
T
S
S
V
and R
V
OUT
0.1μF
0.1μF
IN
13
14
15
16
Figure 4. Calculate Differential Gain
+IN
+IN
–IN
–IN
13
14
15
16
F
=
. For example, when R
+IN
+IN
–IN
–IN
R
100Ω
100Ω
S
2000
100Ω
100Ω
+
T
IN+
IN–
are determined by the combination
200 25
IN+
IN–
1000Ω
1000Ω
•
OUT–
OUT+
1000Ω
1000Ω
R
+
OUT–
OUT+
L
R
L
12.5Ω
12.5Ω
50Ω
50Ω
S
is 50Ω, it is found
12.5Ω
12.5Ω
LTC6401-20
50Ω
50Ω
1.7pF
+OUTF
–OUTF
+OUT
–OUT
LTC6401-20
640120 F04
1.7pF
+OUTF
–OUTF
640120 F03
+OUT
–OUT
8
7
6
5
1/2 R
1/2 R
V
OUT
8
7
6
5
L
L
T
is
input Smith Chart, based on which users can choose the
optimal source impedance for a given gain and noise
requirement.
Output Match and Filter
The LTC6401-20 can drive an ADC directly without
external output impedance matching. Alternatively, the
differential output impedance of 25Ω can be matched to
higher value impedance, e.g. 50Ω, by series resistors or
an LC network.
The internal low pass fi lter outputs at +OUTF/–OUTF
have a –3dB bandwidth of 590MHz. External capacitor
can reduce the low pass 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. LTC6401-20 Internal Filter Topology Modifi ed for Low
Filter Bandwidth (Three External Capacitors)
13
14
15
16
Figure 6. LTC6401-20 Application Circuit for Bandpass
Filtering (Three External Capacitors, One External Inductor)
13
14
15
16
+IN
+IN
–IN
–IN
+IN
+IN
–IN
–IN
100Ω
100Ω
100Ω
100Ω
IN+
IN–
IN+
IN–
1000Ω
1000Ω
1000Ω
1000Ω
OUT–
OUT+
OUT–
OUT+
12.5Ω
12.5Ω
50Ω
50Ω
LTC6401-20
12.5Ω
12.5Ω
50Ω
50Ω
1.7pF
+OUTF
–OUTF
+OUT
–OUT
640120 F06
LTC6401-20
LTC6401-20
1.7pF
+OUTF
–OUTF
8
7
6
5
+OUT
–OUT
640120 F05
10Ω
10Ω
16nH
39pF
39pF
8
7
6
5
39pF
4.99Ω
4.99Ω
12pF
8.2pF
8.2pF
FILTERED OUTPUT
(87.5MHz)
11
LTC2208
640120f