LT6600-10 Linear Technology, LT6600-10 Datasheet - Page 8

• Manufacturer Part Number: LT6600-10
• Description: Very Low Noise Differential Amplifier and 10MHz Lowpass Filter
• Manufacturer: Linear Technology

LT6600-10
the passband flatness near 10MHz. The common mode
output voltage is set to 2V.
Use Figure 4 to determine the interface between the
LT6600-10 and a current output DAC. The gain, or “trans-
impedance”, is defined as A = V
transimpedance, use the following equation:
By setting R1 + R2 = 402 , the gain equation reduces to
A = R1 .
The voltage at the pins of the DAC is determined by R1,
R2, the voltage on Pin 7 and the DAC output current (I
or I
348 . The voltage at Pin 7 is 1.65V. The voltage at the
DAC pins is given by:
I
50.4 .
Evaluating the LT6600-10
The low impedance levels and high frequency operation of
the LT6600-10 require some attention to the matching
networks between the LT6600-10 and other devices. The
previous examples assume an ideal (0 ) source imped-
ance and a large (1k ) load resistance. Among practical
examples where impedance must be considered is the
evaluation of the LT6600-10 with a network analyzer.
8
APPLICATIO S I FOR ATIO
IN
A
V
is I
IN
DAC
–
IN
). Consider Figure 4 with R1 = 49.9
CURRENT
402
OUTPUT
R
–
DAC
1
or I
V
103
•
PIN
R
R
IN
2
mV I
1
I
I
7
IN
IN
+
.The transimpedance in this example is
–
+
•
R
U
R1
R1
1
IN
43 6
R
0.01 F
R
Figure 4
2 402
R2
R2
1
.
U
OUT
1
7
2
8
/I
I
–
+
LT6600-10
IN
W
IN
3.3V
3
6
R
R R
+
–
6600 F04
0.1 F
1
1
. To compute the
4
5
•
R
2
2
V
V
and R2 =
U
OUT
OUT
+
–
IN
+
Figure 5 is a laboratory setup that can be used to charac-
terize the LT6600-10 using single-ended instruments with
50 source impedance and 50 input impedance. For a
unity gain configuration the LT6600-10 requires a 402
source resistance yet the network analyzer output is
calibrated for a 50 load resistance. The 1:1 transformer,
53.6
above. The transformer converts the single-ended source
into a differential stimulus. Similarly, the output the
LT6600-10 will have lower distortion with larger load
resistance yet the analyzer input is typically 50 . The 4:1
turns (16:1 impedance) transformer and the two 402
resistors of Figure 5, present the output of the LT6600-10
with a 1600 differential load, or the equivalent of 800
to ground at each output. The impedance seen by the
network analyzer input is still 50 , reducing reflections in
the cabling between the transformer and analyzer input.
Differential and Common Mode Voltage Ranges
The differential amplifiers inside the LT6600-10 contain
circuitry to limit the maximum peak-to-peak differential
voltage through the filter. This limiting function prevents
excessive power dissipation in the internal circuitry
and provides output short-circuit protection. The limiting
function begins to take effect at output signal levels above
2V
illustrated in Figure 6; the LTC6600-10 was configured
with unity passband gain and the input of the filter was
driven with a 1MHz signal. Because this voltage limiting
takes place well before the output stage of the filter
reaches the supply rails, the input/output behavior of the
IC shown in Figure 6 is relatively independent of the power
supply voltage.
NETWORK
ANALYZER
SOURCE
P-P
50
and it becomes noticeable above 3.5V
and 388
53.6
TTWB-1010
COILCRAFT
1:1
resistors satisfy the two constraints
388
388
Figure 5
1
7
2
8
LT6600-10
+
–
– 2.5V
3
6
2.5V
+
–
0.1 F
0.1 F
4
5
www.DataSheet4U.com
402
402
COILCRAFT
TTWB-16A
4:1
P-P
. This is
NETWORK
ANALYZER
INPUT
6600 F05
50
6600f