AD8045ACPZ-REEL Analog Devices Inc, AD8045ACPZ-REEL Datasheet - Page 20

• Manufacturer Part Number: AD8045ACPZ-REEL
• Description: IC,Operational Amplifier,SINGLE,BIPOLAR,LLCC,8PIN,PLASTIC
• Manufacturer: Analog Devices Inc

Specifications of AD8045ACPZ-REEL

• Amplifier Type: Voltage Feedback
• Number Of Circuits: 1
• Slew Rate: 1350 V/µs
• -3db Bandwidth: 1GHz
• Current - Input Bias: 2µA
• Voltage - Input Offset: 200µV
• Current - Supply: 16mA
• Current - Output / Channel: 70mA
• Voltage - Supply, Single/dual (±): 3.3 V ~ 12 V, ±1.65 V ~ 6 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-LFCSP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Output Type: -
• Gain Bandwidth Product: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD8045
90 MHZ ACTIVE LOW-PASS FILTER (LPF)
Active filters are used in many applications such as antialiasing
filters and high frequency communication IF strips.
With a 400 MHz gain bandwidth product and high slew rate,
the AD8045 is an ideal candidate for active filters. Figure 70
shows the frequency response of the 90 MHz LPF. In addition to
the bandwidth requirements, the slew rate must be capable of
supporting the full power bandwidth of the filter. In this case, a
90 MHz bandwidth with a 2 V p-p output swing requires at least
1200 V/µs. This performance is achievable only at 90 MHz
because of the AD8045’s wide bandwidth and high slew rate.
The circuit shown in Figure 73 is a 90 MHz, 4-pole, Sallen-Key,
LPF. The filter comprises two identical cascaded Sallen-Key LPF
sections, each with a fixed gain of G = +2. The net gain of the
filter is equal to G = +4 or 12 dB. The actual gain shown in
Figure 70 is only 6 dB. This is due to the output voltage being
divided in half by the series matching termination resistor, R
and the load resistor.
–100
–120
Figure 69. Single-Tone FFT, F
–20
–40
–60
–80
0
0
5
Shown in the First Nyquist Zone
10
FREQUENCY (MHz)
IN
15
= 50 MHz, Sample Rate = 65 MSPS
20
SFDR = 65.3dBc
SNR = 69.9dBc
25
A
IN
= –1dBFS
30
Rev. A | Page 20 of 24
T
,
Setting the resistors and capacitors equal to each other greatly
simplifies the design equations for the Sallen-Key filter. The
corner frequency, or −3 dB frequency, can be described by the
equation
The quality factor, or Q, is shown in the equation
The gain, or K, of the circuits are
Resistor values are kept low for minimal noise contribution,
offset voltage, and optimal frequency response. Due to the low
capacitance values used in the filter circuit, the PCB layout and
minimization of parasitics is critical. A few picofarads can detune
the filters corner frequency, f
Figure 73 actually incorporate some stray PCB capacitance.
Capacitor selection is critical for optimal filter performance.
Capacitors with low temperature coefficients, such as NPO
ceramic capacitors and silver mica, are good choices for filter
elements.
Q
First
f
–10
–20
–30
–40
–50
–60
–70
–80
–90
c
20
10
=
=
0
3
2π
Stage
−
1
1
RC
K
0.1
Figure 70. 90 MHz Low-Pass Filter Response
K
=
R4
R3
+
1
1,
FREQUENCY (MHz)
Second
c
. The capacitor values shown in
10
Stage
K
100
=
R8
R7
+
1
1000