Datasheet

y(n) +
ǒ
1
2
11
Ǔ
[h0 x(n) ) h1 x(n * 1) ) h2 x(n * 2) ) AAA ) h11 x(n * 11) ) h11 x(n * 12) ) AAA ) h1 x(n * 22) ) h0 x(n * 23)]
y(n) +
ǒ
1
2
11
Ǔ
x[h0 x(n) ) h1 x(n * 1) ) h2 x(n * 2) ) AAA ) h10 x(n * 10) ) h11 x(n * 11) ) h10 x(n * 12) ) AAA ) h1 x(n * 21) ) h0 x(n * 22)]
ADS62P45, ADS62P44
ADS62P43, ADS62P42
www.ti.com SLAS561C –JULY 2007– REVISED FEBRUARY 2012
Decimation Filters
ADS62P4X includes option to decimate the ADC output data with in-built low pass, high pass or band pass
filters.
The decimation rate and type of filter can be selected using register bits ( DECIMATION RATE) and (
DECIMATION FILTER TYPE). Decimation rates of 2, 4, or 8 are available and either low pass, high pass or band
pass filters can be selected (see Table 24). By default, the decimation filter is disabled – use register bit
<FILTER ENABLE> to enable it.
Table 24. Decimation Filter Modes
COMBINATION OF DECIMATION RATES AND FILTER TYPES <DECIMATIO <FILTER
<DECIMATION N FILTER COEFF <FILTER
RATE> FREQ SELECT ENABLE>
DECIMATION TYPE OF FILTER
BAND> >
Decimate by 2 In-built low-pass filter (pass band = 0 to Fs/4) 0 0 0 0 0 0 1
In-built high-pass filter (pass band = Fs/4 to Fs/2) 0 0 0 0 1 0 1
Decimate by 4 In-built low-pass filter (pass band = 0 to Fs/8) 0 0 1 0 0 0 1
0 0 1 0 1 0 1
In-built 2
nd
band-pass filter (pass band = Fs/8 to Fs/4)
0 0 1 1 0 0 1
In-built 3
rd
band-pass filter (pass band = Fs/4 to 3Fs/8)
In-built last band-pass filter (pass band = 3Fs/8 to Fs/2) 0 0 1 1 1 0 1
Decimate by 2 Custom filter (user programmable coefficients) 0 0 0 X X 1 1
Decimate by 4 Custom filter (user programmable coefficients) 0 0 1 X X 1 1
Decimate by 8 Custom filter (user programmable coefficients) 1 0 0 X X 1 1
No decimation Custom filter (user programmable coefficients) 0 1 1 X X 1 0
Decimation Filter Equation
The decimation filter is implemented as 24-tap FIR with symmetrical coefficients (each coefficient is 12-bit
signed). The filter equation is:
(3)
By setting the register bit <ODD TAP ENABLE> = 1, a 23-tap FIR is implemented:
(4)
In the above equations,
h0, h1 …h11 are 12-bit signed representation of the coefficients,
x(n) is the input data sequence to the filter
y(n) is the filter output sequence
Pre-defined Coefficients
The in-built filter types (low pass, high pass, and band pass) use pre-defined coefficients. The frequency
response of the in-built filters is shown in Figure 102 and Figure 103.
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Product Folder Link(s): ADS62P45, ADS62P44 ADS62P43, ADS62P42