lt1993-2 Linear Technology Corporation, lt1993-2 Datasheet - Page 17

• Manufacturer Part Number: lt1993-2
• Description: 800mhz Low Distortion, Low Noise Differential Ampli? Er/ Adc Driver Av = 2v/v
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
Output Common Mode Adjustment
The LT1993-2’s output common mode voltage is set by the
V
the output common mode voltage anywhere in a range
from 1.1V to 3.6V. Bandwidth of the V
300MHz, so for applications where the V
a DC bias voltage, a 0.1µF capacitor at this pin is recom-
mended. For best distortion performance, the voltage at
the V
When interfacing with most ADCs, there is generally a
V
of the ADC. For 5V ADCs such as the LTC17XX family, this
V
addition of a 0.1µF capacitor) to the input V
LT1993-2. For 3V ADCs such as the LTC22XX families,
the LT1993-2 will function properly using the 1.65V from
the ADC’s V
Dynamic Range (SFDR) and distortion performance can
be achieved by level-shifting the LTC22XX’s V
voltage up to at least 1.8V. This can be accomplished as
shown in Figure 10 by using a resistor divider between
the LTC22XX’s V
ing the LT1993-2’s V
common mode voltage above 1.9V, AC coupling capacitors
are recommended between the LT1993-2 and LTC22XX
IF IN
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0.1µF
80.6Ω
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pin. It is a high-impedance input, capable of setting
output pin that is at about half of the supply voltage
output pin should be connected directly (with the
Figure 10. Level Shifting 3V ADC V
Improved SFDR
pin should be between 1.8V and 2.6V.
13
14
15
16
CM
–INB
–INA
+INB
+INA
reference pin, but improved Spurious Free
CM
+OUTFILTERED
–OUTFILTERED
LT1993-2
V
U
2
output pin and V
OCM
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pin with a 0.1µF capacitor. For a
U
6
7
0.1µF
10Ω
10Ω
W
CC
CM
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and then bypass-
1
2
Voltage for
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AIN
AIN
pin is typically
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CM
+
–
pin is tied to
4.02k
11k
LTC22xx
U
pin of the
reference
31
V
3V
CM
1.5V
1.9V
19932 F10
ADCs because of the input voltage range constraints of
the ADC.
Large Output Voltage Swings
The LT1993-2 has been designed to provide the 3.2V
output swing needed by the LTC1748 family of 14-bit
low-noise ADCs. This additional output swing improves
system SNR by up to 4dB. Typical performance curves
and AC specifi cations have been included for these ap-
plications.
Input Bias Voltage and Bias Current
The input pins of the LT1993-2 are internally biased to
the voltage applied to the V
resistors are needed, even for AC-coupled operation. The
input bias current is determined by the voltage difference
between the input common mode voltage and the V
(which sets the output common mode voltage). At both
the positive and negative inputs, any voltage difference is
imposed across 200Ω, generating an input bias current.
For example, if the inputs are tied to 2.5V with the V
pin at 2.2V, then a total input bias current of 1.5mA will
fl ow into the LT1993-2’s +INA and +INB pins. Furthermore,
an additional input bias current totaling 1.5mA will fl ow
into the –INA and –INB inputs.
Application (Demo) Boards
The DC800A Demo Board has been created for stand-alone
evaluation of the LT1993-2 with either single-ended or
differential input and output signals. As shown, it accepts
a single-ended input and produces a single-ended output
so that the LT1993-2 can be evaluated using standard
laboratory test equipment. For more information on this
Demo Board, please refer to the Demo Board section of
this data sheet.
There are also additional demo boards available that
combine the LT1993-2 with a variety of different Linear
Technology ADCs. Please contact the factory for more
information on these demo boards.
OCM
pin. No external biasing
LT1993-2
17
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19932fa
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pin
P-P