LTC2351-14 Linear Technology, LTC2351-14 Datasheet - Page 15

• Manufacturer Part Number: LTC2351-14
• Description: 1.5Msps Simultaneous Sampling ADC
• Manufacturer: Linear Technology

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APPLICATIO S I FOR ATIO
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
235114 G20
DD
U
.
+
minus
Figure 4 shows the ideal input/output characteristics for
the LTC2351-14 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 LTC2351-14. The LTC2351-14 has 0.7 LSB
RMS of Gaussian white noise.
Figure 5 shows the ideal input/output characteristics for
the LTC2351-14 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 LTC2351-14. The LTC2351-14 has 0.7 LSB
RMS of Gaussian white noise.
Figure 5. LTC2351-14 Transfer Characteristic
in Bipolar Mode (BIP = High)
011...111
011...110
011...101
100...010
100...001
100...000
Figure 4. LTC2351-14 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)
LTC2351-14
FS – 1LSB
FS – 1LSB
235114 F05
235114 F04
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