RHF1401

Application information

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levels will introduce more distortion.

7.1.2

Driving the analog inputs

The RHF1401 is designed to be differentially driven for better noise immunity.

Measurements done with single-ended signals show reduced levels of performance.

The switch-capacitor input structure of RHF1401 has a high input impedance (3.3 k

Ω at

because, at the end of each conversion, the charge update of the sampling capacitor draws

or injects a small transient current on the input signal.

One method of masking this transient current is a low-pass RC filter as shown in Figure 21

and Figure 22. A capacitor with a higher value than the sampling capacitor of 2.4 pF,

mounted in parallel with the two analog input signals, will absorb the transient glitches.

Figure 20.

ADC input equivalent circuit

Figure 18.

(1)

Figure 19.

Distortion vs. Fs

(1)

1.

65

68

71

74

77

80

3

5

7

9

11

13

15

17

19

21

Fs (Mhz)

11.1

11.2

11.3

11.4

11.5

11.6

11.7

11.8

11.9

12

12.1

ENOB

SINAD

SNR

-100

-95

-90

-85

-80

-75

-70

3579

11

13

15

17

19

21

Fs (Mhz)

THD

SFDR

Cs=2.4pF

VIN

VIN

AGND