LTC2379CDE-18 LINEAR [Linear Integrated Systems], LTC2379CDE-18 Datasheet - Page 12

• Manufacturer Part Number: LTC2379CDE-18
• Description: LTC2379-1818-Bit, 1.6Msps, Low Power SAR ADC with 101.2dB SNR
• Manufacturer: LINEAR [Linear Integrated Systems]

LTC2379-18
APPLICATIONS INFORMATION
R1, R2, R3 and R4 must be selected in relation to R
achieve the desired attenuation and to maintain a balanced
input impedance in the first amplifier. Table 1 shows the
resulting SNR and THD for several values of R
R3 and R4 in this configuration. Figure 6b shows the re-
sulting FFT when using the LT6350 as shown in Figure 6a.
Table 1. SNR, THD vs R
Fully Differential Inputs
To achieve the full distortion performance of the
LTC2379-18, a low distortion fully differential signal source
driven through the LT6203 configured as two unity gain
buffers as shown in Figure 7 can be used to get the full
data sheet THD specification of –120dB.
12
100k
10k
R
(Ω)
5V
0V
2k
Figure 5a. LT6350 Converting a 0V-5V Single-Ended
Signal to a ±5V Differential Input Signal
IN
Figure 5b. 32k Point FFT Plot with f
for Circuit Shown in Figure 5a
2.49k
24.9k
499
(Ω)
R1
–100
–120
–140
–160
–180
–20
–40
–60
–80
LT6350
0
8
1
0
+
–
100 200 300 400
2.49k
24.9k
(Ω)
499
R2
IN
for ±10V Single-Ended Input Signal.
FREQUENCY (kHz)
R
INT
100k
(Ω)
10k
R3
2k
+
–
2
V
R
CM
–
+
INT
500
SNR = 101dB
THD = –111.5dB
SINAD = 100.8dB
SFDR = 114.5dB
= V
402
REF
(Ω)
20k
600
R4
2k
/2
700
237918 F05b
4
5
IN
= 2kHz
OUT1
OUT2
800
100.8
100.5
SNR
(dB)
94.8
IN
, R1, R2,
237918 F05a
THD
(dB)
–99
–94
–96
5V
0V
5V
0V
IN
to
Digital Gain Compression
The LTC2379-18 offers a digital gain compression (DGC)
feature which defines the full-scale input swing to be be-
tween 10% and 90% of the ±V
enable digital gain compression, bring the REF/DGC pin
low. This feature allows the LT6350 to be powered off of
a single +5.5V supply since each input swings between
0.5V and 4.5V as shown in Figure 8. Needing only one
Figure 6a. LT6350 Converting a ±10V Single-Ended Signal to
a ±5V Differential Input Signal
Figure 7. LT6203 Buffering a Fully Differential Signal Source
–10V
10V
0V
10μF
V
5V
0V
5V
0V
CM
Figure 6b. 32k Point FFT Plot with f
for Circuit Shown in Figure 6a
R2 = 499Ω
R4 = 402Ω
R3 = 2k
200pF
–100
–120
–140
–160
–180
–20
–40
–60
–80
R
IN
0
0
= 2k
100 200 300 400
LT6350
8
1
LT6203
R1 = 499Ω
+
–
220pF
FREQUENCY (kHz)
3
2
5
6
R
+
–
+
–
INT
+
–
2
REF
500
SNR = 100.8dB
THD = –99.3dB
SINAD = 97.8dB
SFDR = 101.2dB
R
V
CM
INT
–
+
600
analog input range. To
= V
1
7
REF
700
237918 F06b
IN
/2
4
5
= 2kHz
800
OUT1
OUT2
237918 F07
5V
0V
5V
0V
237918 F06a
237918fa
5V
0V
5V
0V