LMH6619
0.1 PF
10 PF
0.1 PF
V
+
1.24 k:
1 nF
150 pF
549:
V
+
-
+
22:
390 pF
14.3 k:
5.6 PF
14.3 k:
1 PF 549:
ADC121S705
0.1 PF
10 PF
V
+
LMH6619
0.1 PF
10 PF
0.1 PF
V
+
1.24 k:
1 nF
150 pF
549:
V
+
-
+
14.3 k:
5.6 PF
14.3 k:
1 PF 549:
22:
390 pF
+IN
-IN
LMH6619Q
www.ti.com
SNOSC78A –JUNE 2012–REVISED NOVEMBER 2012
Table 1. Performance Data for the Single to Differential ADC Driver (continued)
Parameter Measured Value
SINAD 67.9 dB
SNR 68.29 dB
THD −78.6 dB
SFDR 75.0 dB
ENOB 11.0 bits
DIFFERENTIAL ADC DRIVER
Its low noise and wide bandwidth make the LMH6619Q an excellent choice for driving a 12-bit ADC. Figure 5
shows the LMH6619Q driving an ADC121S705. The ADC121S705 is a fully differential 12-bit ADC.The
LMH6619Q is set up in a 2nd order multiple-feedback configuration with a gain of −1. The −3 dB point is at 500
kHz and the −0.01 dB point is at 100 kHz. The 22Ω resistor and 390 pF capacitor form an antialiasing filter for
the ADC121S705. The capacitor also stores and delivers charge to the switched capacitor input of the ADC. The
capacitive load on the LMH6619Q created by the 390 pF capacitor is decreased by the 22Ω resistor. Table 2
shows the performance data.
Figure 5. LMH6619Q Driving an ADC121S705
Table 2. Performance Data for the Differential ADC Driver
Parameter Measured Value
Signal Frequency 100 kHz
SINAD 71.5 dB
SNR 71.87 dB
THD −82.4 dB
Copyright © 2012, Texas Instruments Incorporated Submit Documentation Feedback 19
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