LTC2378-16
applicaTions inForMaTion
V
CM
LT6350
5V
0V
OUT1
4
5V
0V
R2 = 499Ω
R
R
INT
INT
200pF
8
1
+
–
LT6350
5V
0V
OUT1
OUT2
4
5
5V
0V
–
+
R
INT
R
INT
8
+
–
OUT2
5
10µF
R4 = 402Ω
R3 = 2k
2
5V
0V
–
+
+
–
V
= V /2
REF
CM
1
2
237816 F05a
10V
0V
–10V
R
= 2k
R1 = 499Ω
IN
+
–
V
= V /2
REF
CM
Figure .a0 5T63.± Converting a ±V-.V Single-Ended
Signal to a ±.V Differential Input Signal
220pF
237816 F06a
Figure 6a0 5T63.± Converting a ±1±V Single-Ended Signal to
a ±.V Differential Input Signal
0
SNR = 96.5dB
–20
–40
THD = –108.7dB
SINAD = 96.2dB
SFDR = 109.4dB
0
SNR = 96.3dB
–20
–40
THD = –100.9dB
SINAD = 95.2dB
SFDR = 103.3dB
–60
–80
–60
–100
–120
–140
–160
–180
–80
–100
–120
–140
–160
–180
0
100
200
300
400
500
FREQUENCY (kHz)
237816 F05b
0
100
200
300
400
500
Figure .b0 32k Point FFT Plot with fIN = 2kHz
for Circuit Shown in Figure .a
FREQUENCY (kHz)
237816 F06b
Figure 6b0 32k Point FFT Plot with fIN = 2kHz
for Circuit Shown in Figure 6a
R1, R2, R3 and R4 must be selected in relation to R to
ꢁI
achievethedesiredattenuationandtomaintainabalanced
input impedance in the first amplifier. Table 1 shows the
5V
LT6203
5V
0V
3
2
+
–
resulting SIR and THD for several values of R , R1, R2,
ꢁI
1
7
0V
R3 and R4 in this configuration. Figure 6b shows the re-
sulting FFT when using the LT635± as shown in Figure 6a.
5V
0V
5V
0V
5
6
+
–
Table 10 SNR, THD vs RIN for ±1±V Single-Ended Input Signal0
R
R1
ꢁΩx
R2
ꢁΩx
R3
ꢁΩx
R4
ꢁΩx
SNR
ꢁdꢀx
THD
ꢁdꢀx
IN
ꢁΩx
237816 F07
2k
499
499
2k
4±2
2k
96.3
96.3
96.3
–1±1
–92
Figure 70 5T62±3 ꢀuffering a Fully Differential Signal Source
1±k
1±±k
2.49k
24.9k
2.49k
24.9k
1±k
1±±k
2±k
–98
Digital Gain Compression
The LTC2378-16 offers a digital gain compression (DGC)
feature which defines the full-scale input swing to be be-
Fully Differential Inputs
tween 1±% and 9±% of the ±V analog input range. To
REF
To achieve the full distortion performance of the
LTC2378-16,alowdistortionfullydifferentialsignalsource
driven through the LT62±3 configured as two unity gain
buffers as shown in Figure 7 can be used to get the full
data sheet THD specification of –122dꢀ.
enable digital gain compression, bring the REF/DGC pin
low. This feature allows the LT635± to be powered off of
a single +5.5V supply since each input swings between
±.5V and 4.5V as shown in Figure 8. Ieeding only one
237816f
12
LINEAR_DIMENSIONS [ Linear Dimensions ]
