Datasheet

LTC2389-18
22
238918f
applicaTions inFormaTion
Figure 6a. LT6231 Buffering a Fully-Differential or Single-Ended Signal Source
Figure 6b. 32k Point FFT f
SMPL
= 2.5Msps,
f
IN
= 2kHz, for Circuit Shown in Figure 6a;
Driven with Fully Differential Inputs
Figure 6c. 32k Point FFT f
SMPL
= 2.5Msps,
f
IN
= 2kHz, for Circuit Shown in Figure 6a;
Driven with Unipolar Inputs
Figure 6d. 32k Point FFT f
SMPL
= 2.5Msps,
f
IN
= 2kHz, for Circuit Shown in Figure 6a;
Driven with Bipolar Inputs
238918 F06a
IN
IN
+
1nF
15Ω
15Ω
1/2 LT6231
LOWPASS FILTERS
1/2 LT6231
LTC2389-18
1nF
+
+
49.9Ω
49.9Ω
4.096V
0V
0V
4.096V
0V
4.096V
0V
4.096V
0V
2.048V
FREQUENCY (kHz)
0
AMPLITUDE (dBFS)
–60
–40
–20
–80
–100
500250 750 1000 1250
–160
–180
–120
0
–140
238918 F06b
SNR = 99.2dB
THD = –116dB
SINAD = 99.1dB
SFDR = 117dB
FREQUENCY (kHz)
0
AMPLITUDE (dBFS)
–60
–40
–20
–80
–100
500250 750 1000 1250
–160
–180
–120
0
–140
238918 F06c
SNR = 93.8dB
THD = –111dB
SINAD = 93.7dB
SFDR = 112dB
FREQUENCY (kHz)
0
AMPLITUDE (dBFS)
–60
–40
–20
–80
–100
500250 750 1000 1250
–160
–180
–120
0
–140
238918 F06d
SNR = 94.2dB
THD = –109dB
SINAD = 94.1dB
SFDR = 110dB
In applications where slightly degraded SNR and
THD performance is acceptable, it is possible to drive
the LTC2389-18 using the lower power LT6231 ADC
driver configured as two unity-gain buffers, as shown in
Figure6a. The RC time constant of the output lowpass
filter is larger in this topology to limit the high frequency
noise contribution of the LT6231. As shown in the FFT
plots in Figures 6b-6d, this circuit achieves 99.2dB SNR
and –116dB THD in fully differential input mode, 93.8dB
SNR and –111dB THD in unipolar input mode, and 94.2dB
SNR and –109dB THD in bipolar input mode.