ADS5294_15 Datasheet, PDF (32/81 Pages) Texas Instruments – Octal-Channel 14-Bit 80-MSPS High-SNR and Low-Power ADC

ADS5294
SLAS776D – NOVEMBER 2011 – REVISED SEPTEMBER 2015
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Feature Description (continued)
9.3.3 Digital Highpass IIR Filter
DC offset is often observed at ADC input signals. For example, in ultrasound applications, the DC offset from
variable-gain amplifier (VGA) varies at different gains. Such a variable offset can introduce artifacts in ultrasound
images especially in Doppler modes. Analog filter between ADC and VGA can be used with added noise and
power. Digital filter achieves the same performance as analog filters and has more flexibility in fine tuning
multiple characteristics.
ADS5294 includes optional first-order digital high-pass (HP) IIR filter. Figure 46 shows the device block diagram
and transfer function.
y(n)
=
2^k _[x(n)
2^k +1
-
x(n
-1)+y(n
-1)]
(1)
Figure 46. HP Filter Block Diagram
Figure 47 shows the characteristics at k=2 to 10.
3
0
−3
−6
−9
−12
−15
−18
−21
−24
−27
−30
−33
−36
−39
−42
−45
0.02
0.1
1
Input Signal Frequency (MHz)
K=2
K=3
K=4
K=5
K=6
K=7
K=8
K=9
K=10
10 15
Figure 47. HP Filter Amplitude Response at K = 2 to 10
32
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