Datasheet

LT1468
12
1468fb
APPLICATIONS INFORMATION
The 150µV settling curve in the Typical Performance
Characteristics is measured using the Differential Amplifi er
method of AN74 followed by a clamped, nonsaturating
gain of 100. The total gain of 500 allows a resolution of
100µV/DIV with an oscilloscope setting of 0.05V/DIV
The settling of the DAC I-to-V converter on the front page
was measured using the exact methods of AN74. The
optimum nulling of the DAC output capacitance requires
20pF across the 6k feedback resistor. The theoretical limit
for 16-bit settling is 11.1 times this RC time constant or
1.33µs. The actual settling time is 1.7µs at the output of
the LT1468. The LT1468 is the fastest Linear Technology
amplifi er in this application.
The optional noise fi lter adds a slight delay of 100ns, but
reduces the noise bandwidth to 1.6MHz which increases
the output resolution for 16-bit accuracy.
Distortion
The LT1468 has outstanding distortion performance as
shown in the Typical Performance curves of Total Harmonic
Distortion + Noise vs Frequency and Amplitude. The high
open-loop gain and inherently balanced architecture reduce
errors to yield 16-bit accuracy to frequencies as high as
100kHz. An example of this performance is the Typical
Application titled 100kHz Low Distortion Bandpass Filter.
This circuit is useful for cleaning up the output of a high
performance signal generator such as the B & K type
1051 or HP3326A.
Another key application for LT1468 is buffering the input
to a 16-bit A/D converter. In a gain of 1 or 2 this straight-
forward circuit provides uncorrupted AC and DC levels
to the converter, while buffering the A/D input sample-
and-hold circuit from high source impedance which can
reduce the maximum sampling rate. The front page graph
shows better than 16-bit distortion for a gain of 2 with a
10V
P-P
output.
Q10
I5
I2I1
I4 I6
1468 SS
I3
OUT
Q11
Q8
Q9
Q7
Q6Q1 –IN+IN
V
+
V
–
Q5Q2
Q4
C
BIAS
Q3
SIMPLIFIED SCHEMATIC