AD8032 Analog Devices, AD8032 Datasheet - Page 16

• Manufacturer Part Number: AD8032
• Manufacturer: Analog Devices

Specifications of AD8032

• -3db Bandwidth: 80MHz
• Slew Rate: 35V/µs
• Vos: 1mV
• Ib: 450nA
• # Opamps Per Pkg: 2
• Input Noise (nv/rthz): 15nV/rtHz
• Vcc-vee: 2.7V to 12V
• Isy Per Amplifier: 1.6mA
• Packages: DIP,SOIC,SOP

AD8031/AD8032
APPLICATIONS
A 2 MHz SINGLE-SUPPLY, BIQUAD BAND-PASS
FILTER
Figure 47 shows a circuit for a single-supply, biquad band-pass
filter with a center frequency of 2 MHz. A 2.5 V bias level is
easily created by connecting the noninverting inputs of all three
op amps to a resistor divider consisting of two 1 kΩ resistors
connected between 5 V and ground. This bias point is also
decoupled to ground with a 0.1 μF capacitor. The frequency
response of the filter is shown in Figure 48.
To maintain an accurate center frequency, it is essential that the
op amp have sufficient loop gain at 2 MHz. This requires the
choice of an op amp with a significantly higher unity gain,
crossover frequency. The unity gain, crossover frequency of the
AD8031/AD8032 is 40 MHz. Multiplying the open-loop gain by
the feedback factors of the individual op amp circuits yields the
loop gain for each gain stage. From the feedback networks of
the individual op amp circuits, it can be seen that each op amp
has a loop gain of at least 21 dB. This level is high enough to
ensure that the center frequency of the filter is not affected by
the op amp’s bandwidth. If, for example, an op amp with a gain
bandwidth product of 10 MHz was chosen in this application,
the resulting center frequency would shift by 20% to 1.6 MHz.
V
IN
0.1µF
Figure 47. A 2 MHz, Biquad Band-Pass Filter Using AD8031/AD8032
3kΩ
R1
1kΩ
1kΩ
2kΩ
R2
5V
50pF
AD8031
C1
0.1µF
V
OUT
2kΩ
R3
5V
1kΩ
AD8032
R6
2kΩ
R4
0.1µF
1/2
2kΩ
R5
50pF
C2
AD8032
1/2
Rev. D | Page 16 of 20
HIGH PERFORMANCE, SINGLE-SUPPLY LINE DRIVER
Even though the AD8031/AD8032 swing close to both rails, the
AD8031 has optimum distortion performance when the signal
has a common-mode level half way between the supplies and
when there is about 500 mV of headroom to each rail. If low
distortion is required in single-supply applications for signals
that swing close to ground, an emitter-follower circuit can be
used at the op amp output.
Figure 49. Low Distortion Line Driver for Single-Supply, Ground Referenced Signals
Figure 49 shows the AD8031 configured as a single-supply, gain-
of-2 line driver. With the output driving a back-terminated
50 Ω line, the overall gain from V
to minimizing reflections, the 50 Ω back termination resistor
protects the transistor from damage if the cable is short circuited.
The emitter follower, which is inside the feedback loop, ensures
that the output voltage from the AD8031 stays about 700 mV
above ground. Using this circuit, low distortion is attainable
even when the output signal swings to within 50 mV of ground.
The circuit was tested at 500 kHz and 2 MHz.
V
IN
–10
–20
–30
–40
–50
Figure 48. Frequency Response of 2 MHz Band-Pass Filter
0
10k
49.9Ω
2.49kΩ
3
2
100k
7
4
0.1µF
10µF
AD8031
2.49kΩ
5V
6
FREQUENCY (Hz)
1M
2N3904
200Ω
IN
49.9Ω
to V
OUT
10M
is unity. In addition
49.9Ω
100M
V
OUT