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Mini Tutorial
MT-234
One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com
The filter is composed of two sections: the decimation filter
and the programmable filter. The decimation filter has a fixed
transfer function, and it helps to prevent aliasing into the
programmable block. The programmable filter is an infinite
impulse response (IIR) filter that samples the output of the
decimation filter at ⅛ the sampling rate of the input, and
updates its output at the same rate. The SYNCO terminal
generates a synchronization pulse every time the output
changes, and can be used to reconstruct the filtered signal
synchronously at other discrete-time devices such as ADCs.
Using the ADA2200 as a Time
Domain Filter
by Gustavo Castro,
Analog Devices, Inc.
IN THIS MINI TUTORIAL
This mini tutorial briefly introduces the operation of the
ADA2200 as a programmable filter.
Because the filters in the ADA2200 are determined by a
well-defined set of capacitor arrays, the transfer function
characteristics are repeatable, the filter location can be
manipulated with the input clock, and its operation requires
very low power consumption.
INTRODUCTION
The ADA2200 is a very flexible device that can be used as a
programmable filter by disabling the synchronous demodulator
function. Different filter configurations, such as low-pass, bandpass, high-pass, and band-stop filters can be implemented on
the programmable filter block shown in Figure 1 by writing to
23 different registers via the SPI port or with an EEPROM
during power up/reset. In addition, the frequency location of
the corners or center frequencies can be adjusted by varying the
clock rate fed into CLKIN or by changing the value of the clock
divider.
The goal of this tutorial is to briefly introduce the operation of
the ADA2200 as a programmable filter, and to provide the user
with the register contents to define the filters shown in Table 1.
Table 1.
Filter Type
Band-Pass (BP1)
Band-Pass (BP2)
Low-Pass (LP1)
Low-Pass (LP2)
Notch
1
Order, Q
2nd, Q = 8.4
2nd, Q = 4.3
4th
4th
1st
ADA2200
LPF
OUTP
PROGRAM
FILTER
OUTN
fM
CLKIN
XOUT
÷2m
fSI
÷8
VOCM
90°
fSO
VCM
÷2n+1
CLOCK
GEN
CONTROL
REGISTERS
SYNCO
GND
RCLK/SDO
SPI/I2C
MASTER
RST
BOOT
Figure 1. ADA2200 Simplified Block Diagram
Rev. 0 | Page 1 of 9
SCLK/SCL
SDIO/SDA
CS/A0
12892-001
8
INN
Pass-Band
Gain (dB)
0
0
0
0
0
For example, if fSI = fCLK = 500 kHz, the corner frequency is fSI/32 = 15.625 kHz.
VDD
INP
Corner/Center
Frequency
(Hz)1
fSI/32
fSI/32
fSI/40
fSI/64
fSI/32
MT-234
Mini Tutorial
8fSO – f
f fN = fSO /2 fSO
2 fS
8fSO = fSI
ELIMINATED BY DECIMATION FILTER
8fSO – f
180
GAIN
PHASE
–10
8fSO + f
(A)
fSO – f fSO + f 2fSO – f 2fSO + f
225
0
GAIN (dB)
fSO – f fSO + f 2fSO – f 2fSO + f
10
8fSO + f
135
–20
90
–30
45
–40
0
–50
–45
–60
–90
–70
–135
–80
–180
–90
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
NORMALIZED FREQUENCY (Hz/Nyquist)
0.9
PHASE (Degrees)
The decimation filter helps prevent aliasing from the input
and simplifies the input antialiasing requirements. As shown
in Figure 2, without the decimation filter, all images above the
Nyquist frequency (fSO/2) alias into the pass band. For example,
the output for an input signal of frequency, f, would be identical
to that of an input signal of frequency, f + fSO, and it is impossible
to distinguish between the two by simply looking at the output.
The transfer function for the decimation filter is shown in
Figure 3. As it can be observed, significant attenuation is
introduced for signal frequencies above fSO/4 (half of Nyquist),
and it introduces a linear phase shift. This roll-off and phase
shift need to be considered in the design of programmable
filters.
–225
1.0
12892-003
DECIMATION FILTER
Figure 3. Transfer Function of the Decimation Filter
f
fN
fSO
2fSO
fSI
(B)
12892-002
Disabling the Decimation Filter
Figure 2. Aliasing Rejection with Decimation Filter
The decimation filter removes all the images above fSO/2 and
below fSI − fSO/2. If large signals are expected to fall in this
higher frequency band, it may be necessary to add an
antialiasing filter before the input of the ADA2200. If the
preceding stages are limited in frequency content, a simple
RC network can be used to add additional aliasing rejection.
It is possible to disable the decimation filter; however, that does
not eliminate the decimation action. When the decimation filter
is disabled, the input sampling occurs at the same rate fSI, and
the programmable filter block continues to sample the output
of the decimator block at ⅛ of the input rate. Therefore, the
maximum operation frequency of the IIR continues to be fSI/8.
What is accomplished by disabling the decimator is eliminating
the decimator roll-off and the phase shift introduced by it. This
may be desired if the additional antialiasing is not required.
Disable the decimator by writing a Logic 1 to Register 0x027
Bit 6.
Rev. 0 | Page 2 of 9
Mini Tutorial
MT-234
IIR PROGRAMMABLE FILTER
An IIR filter is a recursive filter. Recursion is analogous to
feedback in a continuous time filter. For this reason, it is
possible to define filters with only a few coefficients, but it is
also possible to create unstable filters. By default, the IIR block
is configured as a band-pass filter with a center frequency at
fSO/8 (fSI/64). Figure 4 shows the transfer function for the default
filter, including the effect of the decimation filter.
10
0
f C = 0.4 × 0.5 f SO = 0.4 × 0.5 × 0.125 f SI = 0.025 × 2 − m f CLK
where:
m is the divider of the clock frequency and can take values of 1,
2, or 8.
fCLK is the frequency of the clock signal applied to CLKIN. If
fCLK = 500 kHz and m = 1, the corner will be located at 12.5 kHz,
fSO = 62.5kHz and fN = 31.25 kHz. With all the parameters
remaining the same, reducing the clock frequency to 100 kHz
would move the corner frequency down to 2.5 kHz.
Note that band-pass or band-stop filters will remain with a
constant Q. This means that if the frequency doubles, the width
of the pass band will double as well. In the case of the notch, the
stop band doubles. This effect is shown in Figure 5.
–10
GAIN (dB)
For example, the corner frequency for a 4th-order low-pass filter
with a corner frequency at fC = 0.4 fN can be calculated by
–20
–30
10
–40
0
FCLK/4 = 100kHz
0.75
1.00
NORMALIZED FREQUENCY (Hz/Nyquist)
Figure 4. Transfer Function of the Default Band-Pass Filter
To modify the IIR filter characteristics, it is necessary to modify
the default filter definition, which is stored in the internal
memory between Register 0x0011 through Register 0x0027.
Note that while the content of these registers define the filter
characteristics, they do not represent the actual filter
coefficients, but the internal configuration of the ADA2200
that generates the coefficients that represent the desired filter.
For detailed instructions on how to access these registers and
change their contents, refer to the Programming IIR Filters
section.
FREQUENCY SCALING
Because the ADA2200 is a sampled analog technology device,
its frequency characteristics directly depend on the clock
frequency. Therefore, parameters such as corner frequency, the
center of the pass band, or the location of the Nyquist frequency
depend on the frequency of the clock used to drive the device.
A natural consequence of this fundamental property is that it is
possible to scale these filters by changing the clock frequency
or using the on-chip clock dividers. This allows the user to
perform frequency sweeps, lock the filter to a source for
coherent filtering, or change the corner frequency without
having to reprogram the device.
–10
–20
–30
–40
–50
0.10
6.25
12.50
18.75
25.00
FREQUENCY (kHz)
12892-005
0.50
Figure 5. Effect of Scaling the Clock Frequency on a Band-Pass Filter
An additional advantage that comes with reducing the clock
frequency is that it lowers the power consumption, thus the
system scales according to the bandwidth of interest.
500
475
450
425
3.3V
400
375
350
2.7V
325
300
275
250
0
200
400
600
CLKIN FREQUENCY (kHz)
800
1000
12892-006
0.25
GAIN (dB)
0
IDD (µA)
–50
12892-004
FCLK = 400kHz
Figure 6. Typical Current Draw vs. CLKIN Frequency at VDD = 2.7 V and 3.3 V
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COHERENT FILTERING AND THE REFERENCE
CLOCK
RECONSTRUCTION OF THE OUTPUT SIGNAL
Certain applications, especially those involving pass-band filters
or notches, require that the signal of interest (or the signal being
rejected) fall precisely at the center frequency of the filter. Any
mismatch between the signal and the center frequency (due to
design tolerances, time and temperature drift, and uncertainty
on the interference source), can cause undesired attenuation
and phase errors in band-pass applications. In the case of a
notch filter (or band stop), these mismatches limit the
effectiveness of the interference rejection, making it very
difficult to completely eliminate undesired signals. This is
shown in Figure 7 for two different notch filters. A narrow
notch is desired to avoid affecting adjacent frequencies, but
its effectiveness is much less than that of the wider notch if
the undesired signal does not match the center.
The output voltage present across the OUTP and OUTN
terminals of ADA2200 is equivalent to the voltage across a
parallel capacitor combination, and therefore, this value
remains constant until the next update cycle. For this reason,
the output signal is formed by a sequence of discrete-time steps,
as shown in Figure 8.
OUTPUT
INPUT
RECONSTRUCTED
100mV/DIV
20µs/DIV
0
Figure 8. Input, Output, and Reconstructed Waveforms
–40
–60
–78dB
fC
10fC
FREQUENCY (Hz)
12892-007
–80
Figure 7. Mismatch Between the Notch Frequency and the
Unwanted Signal Limits Band Stop Effectiveness
In cases where the signal of interest is known, it can be used to
generate a clock signal to drive the ADA2200. As an alternative,
the reference clock can be used to generate a time base for the
signal of interest, synchronization, or to be the actual signal
required as an excitation source, for example. The synchronization between the ADA2200 and the signal in question
guarantees that it will always fall at the center frequency of
the filter.
In a continuous time system, the step sequence generates
images at frequencies multiples of the output update rate. This
effect can be observed in Figure 8, where the vertical lines are a
consequence of the finite bandwidth of the output (the pin
driver is a continuous-time device). The high-frequency image
can be visualized by tracing a sine wave across the output steps
and then subtracting it. The resulting saw-tooth waveform is a
multiple of the fundamental frequency, and it is a typical and
undesired artifact. To reduce undesired images in continuous
time systems, a reconstruction filter is required at the output,
as shown in Figure 9.
+3.3V
INPUT
VDD
INP
OUTP
INN
OUTN
OUTPUT
ADA2200
VOCM
CLKIN
XOUT
VSS
SYNCO
ADA4841-1
SCK
SDI
SDO
CS
12892-009
MAGNITUDE (dB)
–17dB
–20
–100
0.1fC
12892-008
20
Figure 9. Adding a Second-Order Reconstruction Filter
When interfacing to discrete time systems (such as SAR ADCs),
a reconstruction filter is not required if the sampler of the
following device is synchronized with the output. For example,
if a SAR ADC takes only one sample for every output update of
the ADA2200, the signal does not need to be reconstructed and
all the high-frequency images will disappear; the ADC will not
know they ever existed.
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Mini Tutorial
MT-234
The ADA2200 generates an output pulse through the SYNCO
terminal, which can be used by a microprocessor or directly
by an ADC to initiate an analog-to-digital conversion of the
ADA2200 output. The SYNCO signal ensures that the ADC
sampling occurs at an optimal time during the ADA2200 output
sample window by generating a pulse with a frequency equal to
the output update rate, fSO. It is possible to configure the pulse
polarity, and to adjust 1 of 16 different timing delays, as shown
in Figure 10. The timing delays are spaced at ½ fSI clock cycle
intervals and span the full output sample window. Choosing the
proper delay relative to the output update ensures a properly
settled signal and avoids feed-through errors in the ADC. The
configuration settings for the SYNCO pulse such as polarity and
delay are contained in Register 0x0029.
INx, OUTx
SYNCO (0)
SYNCO (1)
FILTERING SIGNALS ABOVE NYQUIST
The maximum recommended input sampling frequency for
the ADA2200 is 1 MHz (equivalent to the clock frequency when
the clock divider is set to 1), which would theoretically limit
its bandwidth to fSO/16 or 62.5 kHz. Because the input signal
bandwidth of the ADA2200 is 4 MHz, the ADA2200 will accept
input signals up to this frequency. However, any of such signals
will be down converted at the output, limited by fSO/2 (the
Nyquist frequency of the output update rate). In other words,
for frequencies above Nyquist, the ADA2200 acts as a filter and
a downconversion mixer by taking advantage of the sampling
nature of the input.
For example, let us assume the ADA2200 samples the input at
fSI = fCLK = 500 kHz, and the filter is configured for a center
frequency at 7.8 kHz and pass band from 6 kHz to 10 kHz. If
the decimator filter is enabled, a filter with 4 kHz bandwidth
will appear around the center frequencies such as 492.2 kHz,
507.8 kHz, 992.2 kHz, 1.0078 MHz, 1.4922 MHz. Therefore, if
a signal with a frequency of 3.992 MHz appears at the input of
the ADA2200, it will appear as a 8 kHz signal at the output.
The equivalent Q of the filter image with a center frequency
at 3.9922 MHz for this example will be almost 1000.
It is important to note that in all these cases, there is always
an adjacent filter image below and above any multiple of fSI,
therefore the designer must consider possible aliasing. In
addition, the higher the frequency, the higher the Q that the
antialiasing filter requires.
SYNCO (13)
SYNCO (14)
CLKIN
0
2
4
6
8
10
12
12892-010
SYNCO (15)
Figure 10. SYNCO Output Timing Relative to OUTP/OUTN, INP/INN,
and CLKIN
Rev. 0 | Page 5 of 9
MT-234
Mini Tutorial
PROGRAMMING IIR FILTERS
The test setup is shown in Figure 11. The board can get power
from any active USB port. All the filters are relative to the
400 kHz on-board oscillator. The AD8476-EVALZ and the
EVAL-INAMP-82RZ with the AD8429 coupled the singleended terminals on the network analyzer to the ADA2200.
For additional details and circuit schematics on the ADA2200EVALZ board, refer to the ADA2200-EVALZ user guide.
To program the filter via the SPI port, initiate a write cycle to
transfer the new filter definition to the ADA2200 registers from
Address 0x0011 to Address 0x0027. For a list of filter options
and their corresponding register values, see Table 2. After
loading the filter values, write 0x03 to Register 0x0010 to
configure the ADA2200 with the new filter. For more
information for interfacing via the SPI port, refer to the
ADA2200 data sheet.
HP 3577A NETWORK ANALYZER
To program the ADA2200 via an external EEPROM during
boot or after a reset operation, it is necessary to preload the
EEPROM with the memory configuration between Address
0x0011 to Address 0x002B, which includes the filter definition
plus additional configuration registers. For the default memory
contents and predefined filter definitions, refer to Table 2. For
detailed instructions on how to program the ADA2200, refer to
the Device Configuration section in the ADA2200 data sheet.
OUTPUT
+3.3V
A
+15V
400kHz OSC
P2
The filter measurements in this tutorial were performed with
the ADA2200-EVALZ, by rewriting the contents of the onboard EEPROM with an EEPROM programmer. The EEPROM
contents were the same as in Table 2 for each configuration,
starting at Offset 0x00. Loading the programmed EEPROM on
X1 and setting the EEPROM_BOOT switch automatically loads
the new filter after applying power to the board.
R
P11
AD8429
ADA2200
AD8476-EVALZ
P3
EEPROM
P12
–15V
ADA2200-EVALZ
(POWERED FROM USB)
EVAL-INAMP-RZ
12892-011
AD8476
Figure 11. Test Setup Using ADA2200-EVALZ
The recommended register contents to configure the ADA2200
as a time domain filter are shown in Table 2.
Table 2. Recommended Register Contents for Different Filters
ADA2200 Address
0x0011
0x0012
0x0013
0x0014
0x0015
0x0016
0x0017
0x0018
0x0019
0x001A
0x001B
0x001C
0x001D
0x001E
0x001F
0x0020
0x0021
0x0022
0x0023
0x0024
0x0025
0x0026
0x0027
0x0028
0x0029
0x002A
0x002B
1
Register Name
Filter
configuration
Analog pin configuration
Sync control
Demod control
Clock configuration
BP1
0xC0
0x0F
0x36
0xD1
0xC0
0x0F
0x07
0x80
0x07
0x80
0x00
0x20
0xC0
0x4F
0xAA
0xAA
0xC0
0x0F
0xC0
0x4F
0x23
0x02
0x02
0x00
0x0D
0x08
0x02
BP2
0xC0
0x0F
0xFA
0xD5
0xC0
0x0F
0x15
0x92
0x15
0x92
0x00
0x20
0xC0
0x4F
0xB2
0x2F
0xC0
0x0F
0xC0
0x4F
0x23
0x02
0x02
0x00
0x0D
0x08
0x02
LP1
0x52
0xAE
0x52
0xA6
0x52
0xAE
0x74
0x81
0x74
0x81
0x4E
0x9D
0x22
0x53
0x4F
0x80
0xC0
0x0F
0xF1
0xDE
0x23
0x02
0x12
0x00
0x0D
0x08
0x02
LP2
0x51
0x80
0x40
0x80
0x51
0x80
0x56
0x10
0x56
0x10
0xC8
0xA0
0x97
0xD9
0xED
0x12
0xC0
0x0F
0x00
0xE0
0x23
0x02
0x06
0x00
0x0D
0x08
0x02
The EEPROM is loaded on the X1 position in ADA2200-EVALZ.
Rev. 0 | Page 6 of 9
Notch
0xC0
0x4F
0x84
0x9B
0xC0
0x0F
0xC0
0x0F
0x84
0x9B
0x36
0x14
0xC0
0x0F
0xC0
0x0F
0xC0
0x0F
0xC0
0x4F
0x23
0x02
0x07
0x00
0x0D
0x08
0x02
Default
0xC0
0x0F
0x1D
0xD7
0xC0
0x0F
0xC0
0x0F
0x1D
0x97
0x7E
0x88
0xC0
0x0F
0xC0
0x0F
0xC0
0x0F
0x00
0xE0
0x23
0x02
0x24
0x00
0x2D
0x08
0x02
All-Pass
0x00
0xA0
0xC0
0x0F
0xC0
0x0F
0xC0
0x0F
0xC0
0x0F
0xC0
0x0F
0xC0
0x0F
0xC0
0x0F
0xC0
0x0F
0xC0
0x0F
0x23
0x02
0x00
0x00
0x2D
0x08
0x02
External EEPROM Address1
0x000
0x001
0x002
0x003
0x004
0x005
0x006
0x007
0x008
0x009
0x00A
0x00B
0x00C
0x00D
0x00E
0x00F
0x010
0x011
0x012
0x013
0x014
0x015
0x016
0x017
0x018
0x019
0x01A
Mini Tutorial
MT-234
The following plots show the transfer function characteristics for the filters on Table 2.
90
–20
90
–30
45
–30
45
–40
0
–40
0
–50
–45
–50
–45
–60
–90
–60
–90
–70
–135
–70
–135
–80
–180
–80
–180
–90
–225
1.0
0.2
0.3
0.4
0.5
0.6
0.7
0.8
NORMALIZED FREQUENCY (Hz/Nyquist)
0.9
225
0
180
0
135
–10
10
225
180
GAIN
PHASE
135
90
–30
45
–40
0
–50
–45
–60
–90
–70
–135
–70
–135
–80
–180
–80
–180
–90
–225
1.0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
NORMALIZED FREQUENCY (Hz/Nyquist)
0.9
GAIN (dB)
PHASE (Degrees)
–20
GAIN
PHASE
0
90
45
–40
0
–50
–45
–60
–90
1k
10k
–225
100k
FREQUENCY (Hz)
Figure 13. Transfer Function of the BP2 Filter
10
–20
–30
–90
100
12892-013
GAIN (dB)
–225
100k
Figure 15. Transfer Function of the BP1 Filter, Logarithmic Sweep,
fCLKIN = fSI = 400 kHz
10
GAIN
PHASE
10k
FREQUENCY (Hz)
Figure 12. Transfer Function of the BP1 Filter
–10
1k
Figure 16. Transfer Function of the BP2 Filter, Logarithmic Sweep,
fCLKIN = fSI = 400 kHz
225
10
180
0
225
180
GAIN
PHASE
135
–10
–20
90
–20
90
–30
45
–40
0
PHASE (Degrees)
–10
135
45
–40
0
–50
–45
–50
–45
–60
–90
–60
–90
–70
–135
–70
–135
–80
–180
–80
–180
–90
–225
1.0
0.2
0.3
0.4
0.5
0.6
0.7
0.8
NORMALIZED FREQUENCY (Hz/Nyquist)
0.9
12892-014
0.1
GAIN (dB)
–30
0
PHASE (Degrees)
GAIN (dB)
–90
100
135
PHASE (Degrees)
0.1
PHASE (Degrees)
–10
–20
0
GAIN (dB)
180
GAIN
PHASE
12892-015
0
135
12892-012
GAIN (dB)
180
225
12892-016
GAIN
PHASE
10
Figure 14. Transfer Function of the LP1 Filter
–90
100
1k
10k
–225
100k
FREQUENCY (Hz)
Figure 17. Transfer Function of the LP1 Filter, Logarithmic Sweep,
fCLKIN = fSI = 400 kHz
Rev. 0 | Page 7 of 9
PHASE (Degrees)
0
–10
225
12892-017
10
MT-234
Mini Tutorial
10
225
180
0
180
90
–20
–30
45
–40
0
–50
–45
–60
–90
–70
–135
–80
–180
–90
–225
1.0
0.2
0.3
0.4
0.5
0.6
0.7
0.8
NORMALIZED FREQUENCY (Hz/Nyquist)
0.9
GAIN
PHASE
GAIN (dB)
–50
–45
–60
–90
–70
–135
–80
–180
10
225
180
–10
–20
90
–20
–30
45
–40
0
–50
–45
–60
–90
–70
–135
–80
–180
–90
–225
1.0
0.9
GAIN (dB)
PHASE (Degrees)
0
0.2
0.3
0.4
0.5
0.6
0.7
0.8
NORMALIZED FREQUENCY (Hz/Nyquist)
GAIN
PHASE
0
135
GAIN
PHASE
90
–30
45
–40
0
–50
–45
–60
–90
–70
–135
–80
–180
–90
100
1k
10k
–225
100k
FREQUENCY (Hz)
Figure 19. Transfer Function of the Notch Filter
10
–225
100k
225
135
0.1
10k
Figure 21. Transfer Function of the LP2 Filter, Logarithmic Sweep,
fCLKIN = fSI = 400 kHz
180
0
1k
FREQUENCY (Hz)
12892-019
GAIN (dB)
0
–10
0
Figure 22. Transfer Function of the Notch Filter, Logarithmic Sweep,
fCLKIN = fSI = 400 kHz
225
10
180
0
225
180
135
–10
–20
90
–20
90
–30
45
–30
45
–40
0
–50
–45
–60
–90
–60
–90
–70
–135
–70
–135
–80
–180
–80
–180
–90
–225
1.0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
NORMALIZED FREQUENCY (Hz/Nyquist)
0.9
GAIN (dB)
PHASE (Degrees)
–10
12892-020
GAIN (dB)
45
–40
–90
100
Figure 18. Transfer Function of the LP2 Filter
10
–30
PHASE (Degrees)
0.1
90
12892-023
0
135
GAIN
PHASE
PHASE (Degrees)
–10
–20
12892-022
135
PHASE (Degrees)
–10
12892-018
GAIN (dB)
0
225
GAIN
PHASE
135
–40
0
–50
–45
–90
100
1k
10k
PHASE (Degrees)
GAIN
PHASE
–225
100k
FREQUENCY (Hz)
Figure 23. Transfer Function of the Default Filter, Logarithmic Sweep,
fCLKIN = fSI = 400 kHz
Figure 20. Transfer Function of the Default Filter
Rev. 0 | Page 8 of 9
12892-024
10
MT-234
10
0
225
180
135
–10
–20
90
–20
90
–30
45
–30
45
–40
0
–40
0
–50
–45
–50
–45
–60
–90
–60
–90
–70
–135
–70
–135
–180
–80
–180
GAIN
PHASE
–80
–90
0
0.1
0.8
0.6
0.7
0.5
0.3
0.4
0.2
NORMALIZED FREQUENCY (Hz/Nyquist)
0.9
–225
1.0
GAIN (dB)
PHASE (Degrees)
0
–10
–90
100
180
GAIN
PHASE
135
1k
10k
PHASE (Degrees)
225
–225
100k
FREQUENCY (Hz)
Figure 25. Transfer Function of the All-Pass Filter, Decimator Enabled,
Logarithmic Sweep, fCLKIN = fSI = 400 kHz
Figure 24. Transfer Function of the All-Pass Filter, Decimator Enabled
REVISION HISTORY
12/14—Revision 0: Initial Version
©2014 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
MT12892-0-12/14(0)
Rev. 0 | Page 9 of 9
12892-025
10
12892-021
GAIN (dB)
Mini Tutorial