Datasheet
Table Of Contents
- Features
- Applications
- Functional Block Diagram
- General Description
- Table of Contents
- Electrical Characteristics—20 kΩ, 50 kΩ, 200 kΩ Versions
- Timing Characteristics—20 kΩ, 50 kΩ, 200 kΩ Versions
- Absolute Maximum Ratings
- Pin Configuration and Pin Function Descriptions
- Typical Performance Characteristics
- Test Circuits
- SPI-Compatible Digital Interface (DIS = 0)
- I2C-Compatible Digital Interface (DIS = 1)
- Operation
- Programming the Variable Resistor
- Programming the Potentiometer Divider Voltage Output Operation
- Pin-Selectable Digital Interface
- SPI-Compatible 3-Wire Serial Bus (DIS = 0)
- I2C-Compatible 2-Wire Serial Bus (DIS = 1)
- Additional Programmable Logic Output
- Self-Contained Shutdown Function
- Multiple Devices on One Bus
- Level Shift for Negative Voltage Operation
- ESD Protection
- Terminal Voltage Operating Range
- Power-Up Sequence
- VLOGIC Power Supply
- Layout and Power Supply Bypassing
- RDAC Circuit Simulation Model
- Applications Information
- Bipolar DC or AC Operation from Dual Supplies
- Gain Control Compensation
- Programmable Voltage Reference
- 8-Bit Bipolar DAC
- Bipolar Programmable Gain Amplifier
- Programmable Voltage Source with Boosted Output
- Programmable 4 to 20 mA Current Source
- Programmable Bidirectional Current Source
- Programmable Low-Pass Filter
- Programmable Oscillator
- Resistance Scaling
- Resistance Tolerance, Drift, and Temperature Coefficient Mismatch Considerations
- Outline Dimensions
AD5263 Data Sheet
Rev. F | Page 26 of 28
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
2
2
2
O
O
O
I
O
S
Q
S
V
V
ω
ω
ω
++
=
(10)
C2C1R2R1
O
×××
=
1
ω
(11)
C2R2C1R1
Q
×
+
×
=
11
(12)
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.
03142-064
V
I
U1
V
O
R1
A
R
W
B
R2
A
R
W
B
C2 C
C1
C
+2.5V
V+
V–
–2.5V
AD8601
ADJUSTED TO
SAME SETTING
Figure 65. Sallen-Key Low-Pass Filter
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
O
, the overall phase
shift is zero, and the positive feedback causes the circuit to oscillate.
With R = R′, C = C′, and R2 = R2A||(R2B + R
DIODE
), the oscillation
frequency is
RC
O
1
=
ω
, or
RC
f
O
π
2
1
=
(13)
where R is equal to R
WA
, such that
AB
R
D
R
256
256 −
=
(14)
At resonance, setting
2=
R1
R2
(15)
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
DD
O
VR2BIV +×=
3
2
(16)
V
O
, I
D
, and V
D
are interdependent variables. With proper selection
of R2B, an equilibrium is reached such that V
O
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.
03142-065
FREQUENCY
ADJUSTMENT
2.2nF
C
2.2nF
R’
10kΩ
R
10kΩ
B A
A
W
V+
V–
B
B
W
W
D1
D2
V
O
U
1
VP
A
VN
–2.5V
+2.5V
R1
1kΩ
R2B
10kΩ
R2A
2.1kΩ
R1 = R1
’
= R2B = AD5263
D1 = D2 = 1N4148
AMPLITUDE
ADJUSTMENT
OP1177
Figure 66. Programmable Oscillator with Amplitude Control