LTC1408 LINER [Linear Technology], LTC1408 Datasheet - Page 15

• Manufacturer Part Number: LTC1408
• Description: Channel, 14-Bit, 600ksps Simultaneous Sampling ADC with Shutdown
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
during conversion.
INPUT SPAN VERSUS REFERENCE VOLTAGE
The differential input range has a unipolar voltage span
that equals the difference between the voltage at the
reference buffer output V
ground. The differential input range of the ADC is 0V to
2.5V when using the internal reference. The internal ADC
is referenced to these two nodes. This relationship also
holds true with an external reference.
DIFFERENTIAL INPUTS
The ADC will always convert the difference of CH
CH
of inputs. The common mode rejection holds up at high
frequencies (see Figure 3.) The only requirement is that
both inputs not go below ground or exceed V
Integral nonlinearity errors (INL) and differential nonlin-
earity errors (DNL) are largely independent of the common
mode voltage. However, the offset error will vary. DC
CMRR is typically better than –90dB.
–
, independent of the common mode voltage at any pair
–120
–100
–20
–40
–60
–80
0
100
Figure 3. CMRR vs Frequency
1k
U
10k 100k
FREQUENCY (Hz)
REF
U
(Pin 23) and the voltage at
1M
W
10M 100M 1G
1408 G20
DD
U
.
+
minus
Figure 4 shows the ideal input/output characteristics for
the LTC1408 in unipolar mode (BIP = Low). The code
transitions occur midway between successive integer LSB
values (i.e., 0.5LSB, 1.5LSB, 2.5LSB, FS – 1.5LSB). The
output code is straight binary with 1LSB = 2.5V/16384 =
153µV for the LTC1408. The LTC1408 has 0.7 LSB RMS
of Gaussian white noise.
Figure 5 shows the ideal input/output characteristics for
the LTC1408 in bipolar mode (BIP = High). The code
transitions occur midway between successive integer LSB
values (i.e., 0.5LSB, 1.5LSB, 2.5LSB, FS – 1.5LSB). The
output code is 2’s complement with 1LSB = 2.5V/16384 =
153µV for the LTC1408. The LTC1408 has 0.7 LSB RMS
of Gaussian white noise.
Figure 5. LTC1408 Transfer Characteristic
in Bipolar Mode (BIP = High)
011...111
011...110
011...101
100...010
100...001
100...000
Figure 4. LTC1408 Transfer Characteristic
in Unipolar Mode (BIP = Low)
111...111
111...110
111...101
000...010
000...001
000...000
–FS
0
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
FS – 1LSB
FS – 1LSB
LTC1408
1408 F05
1408 F04
15
1408fa