EVAL-AD5263EBZ Analog Devices Inc, EVAL-AD5263EBZ Datasheet - Page 26

• Manufacturer Part Number: EVAL-AD5263EBZ
• Description: EVALUATION BOARD I.C.
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD5263EBZ

• Main Purpose: Digital Potentiometer
• Embedded: No
• Utilized Ic / Part: AD5263
• Primary Attributes: 4 Channel, 256 Position
• Secondary Attributes: I²C & SPI Interfaces
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD5263
PROGRAMMABLE LOW-PASS FILTER
In analog-to-digital conversion applications, it is common to
include an antialiasing filter to band-limit the sampling signal.
Dual-channel digital potentiometers can be used to construct a
second-order Sallen-Key low-pass filter (see Figure 65). The
design equations are
Users can first select some convenient values for the capacitors.
To achieve maximally flat bandwidth where Q = 0.707, let C1 be
twice the size of C2, and let R1 = R2. As a result, the user can
adjust R1 and R2 to the same settings to achieve the desired
bandwidth.
PROGRAMMABLE OSCILLATOR
In a classic Wien bridge oscillator (Figure 66), the Wien network
(R, R ′ , C, C ′ ) provides positive feedback, while R1 and R2
provide negative feedback. At the resonant frequency, f
overall phase shift is zero, and the positive feedback causes the
circuit to oscillate.
With R = R ′ , C = C ′ , and R2 = R2A||(R2B + R
oscillation frequency is
where R is equal to R
ω
Q
ω
V
R
V
O
O
O
I
=
=
=
=
=
256 −
V
R1
I
RC
256
S
1
×
R1
1
2
C1
+
SAME SETTING
D
ADJUSTED TO
A
, or
×
R
ω
Figure 65. Sallen-Key Low-Pass Filter
R1
Q
R2
R
ω
+
O
W
B
AB
O
f
R2
×
1
WA
S
O
2
C1
+
, such that
1
×
=
A
ω
R
C2
×
R2
2
O
π
C2
W
2
1
B
C2
RC
C
C1
C
AD8601
+2.5V
–2.5V
V+
V–
U1
DIODE
), the
V
O
O
, the
(11)
(12)
(13)
(14)
(15)
Rev. B | Page 26 of 28
At resonance, setting
balances the bridge. In practice, R2/R1 should be set slightly
greater than 2 to ensure that the oscillation can start. On the
other hand, the alternating turn-on of the diodes D1 and D2
ensures that R2/R1 is momentarily less than 2, thereby
stabilizing the oscillation.
Once the frequency is set, the oscillation amplitude can be
tuned by R2B because
V
selection of R2B, an equilibrium is reached such that V
converges. R2B can be in series with a discrete resistor to
increase the amplitude, but the total resistance should not be
so large that it saturates the output.
O
, I
D
R2
2
3
R1
, and V
V
Figure 66. Programmable Oscillator with Amplitude Control
O
=
2.2nF
R1 = R1
D1 = D2 = 1N4148
2
=
I
D
D
are interdependent variables. With proper
’
ADJUSTMENT
×
= R2B = AD5263
FREQUENCY
R2B
10kΩ
R
B
A
+
V
D
W
1kΩ
VN
R1
VP
B
OP1177
W
10kΩ
+2.5V
–2.5V
R2B
2.2nF
C
A
V+
V–
2.1kΩ
R2A
AMPLITUDE
ADJUSTMENT
A
W
U
10kΩ
1
R’
B
D1
D2
V
O
O
(16)
(17)