AD8682ARZ Analog Devices Inc, AD8682ARZ Datasheet - Page 11

• Manufacturer Part Number: AD8682ARZ
• Description: IC OPAMP JFET 3.5MHZ DUAL 8SOIC
• Manufacturer: Analog Devices Inc

Specifications of AD8682ARZ

• Slew Rate: 9 V/µs
• Amplifier Type: J-FET
• Number Of Circuits: 2
• Gain Bandwidth Product: 3.5MHz
• Current - Input Bias: 6pA
• Voltage - Input Offset: 350µV
• Current - Supply: 210µA
• Current - Output / Channel: 12mA
• Voltage - Supply, Single/dual (±): 9 V ~ 36 V, ±4.5 V ~ 18 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Op Amp Type: General Purpose
• No. Of Amplifiers: 2
• Bandwidth: 3.5MHz
• Supply Voltage Range: ± 4.5V To ± 18V
• Amplifier Case Style: SOIC
• No. Of Pins: 8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Output Type: -
• -3db Bandwidth: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

V
PROGRAMMABLE STATE VARIABLE FILTER
The circuit shown in Figure 34 can be used to accurately program
the Q factor; the cutoff frequency, f
state variable filter. The AD8684 has been used in this design
because of its high bandwidth, low power, and low noise. This
circuit takes only three packages to build because of the quad
configuration of the op amps and DACs.
The DACs shown are used in voltage mode; therefore, many
values are dependent on the accuracy of the DAC only and not
on the absolute values of the DAC resistive ladders. As a result, this
makes the circuit unusually accurate for a programmable filter.
Adjusting DAC 1 changes the signal amplitude across R1; therefore,
the DAC attenuation × R1 determines the amount of signal current
that charges the integrating capacitor, C1.
IN
DAC8408
DAC 3
1/4
AD8684
1/4
2kΩ
2kΩ
R5
R6
C
AD8684
; and the gain of a 2-pole
1/4
2kΩ
R4
HIGH PASS
AD8684
2kΩ
R3
1/4
DAC8408
DAC 1
Figure 34. Programmable State Variable Filter
1/4
2kΩ
R2
Rev. A | Page 11 of 16
AD8684
AD8684
1/4
1/4
2kΩ
DAC8408
R1
This cutoff frequency can be expressed as
where D1 is the digital code for the DAC.
DAC3 is used to set the gain. The gain equation is
DAC 2 is used to set the Q of the circuit. Adjusting this DAC
controls the amount of feedback from the band-pass node to
the input summing node. Note that the digital value of the
DAC is in the numerator; therefore, zero code is not a valid
operating point.
DAC 2
1/4
Gain
Q
AD8684
f
1/4
C
1000pF
=
C1
=
R2
R3
2π
=
R5
R4
R1C1
⎛
⎜
⎝
1
256
D2
2kΩ
⎛
⎜
⎝
R7
256
DAC8408
D3
⎞
⎟
⎠
DAC 4
⎛
⎜
⎝
BAND PASS
256
1/4
D1
⎞
⎟
⎠
⎞
⎟
⎠
AD8684
1/4
AD8682/AD8684
2kΩ
R1
AD8684
1/4
1000pF
C1
LOW
PASS