AD8672 Analog Devices, AD8672 Datasheet - Page 14

• Manufacturer Part Number: AD8672
• Description: Dual Precision Very Low Noise, Low Input Bias Current Operational Amplifier
• Manufacturer: Analog Devices

Specifications of AD8672

• -3db Bandwidth: 10MHz
• Slew Rate: 4V/µs
• Vos: 20µV
• Ib: 3nA
• # Opamps Per Pkg: 2
• Input Noise (nv/rthz): 2.8nV/rtHz
• Vcc-vee: 10V to 36V
• Isy Per Amplifier: 3.5mA
• Packages: SOIC,SOP

AD8671/AD8672/AD8674
GPS RECEIVER
GPS receivers require low noise to minimize RF effects. The
precision of the AD8671 makes it an excellent choice for such
applications. Its very low noise and wide bandwidth make it
suitable for band-pass and low-pass filters without the penalty
of high power consumption.
Figure 39 shows a simplified block diagram of a GPS receiver.
The next section details the design equations.
BAND-PASS FILTER
Filters are useful in many applications; for example, band-pass
filters are used in GPS systems, as discussed in the previous
section. Figure 40 shows a second-order band-pass KRC filter.
The equal component topology yields a center frequency
where:
and
K
fo
= 1
=
V
Q
2
IN
+
π
=
BAND-PASS FILTER
RC
R
2
R
4
B
A
2.25kΩ
−
AD8671
2
R1
K
Figure 40. Band-Pass KRC Filter
1nF
C2
C2
1nF
2.25kΩ
R2
LOW NOISE OP AMP
AD8671
2.25kΩ
R3
V
V
CC
EE
R
R
A
B
Figure 39. Simplified Block Diagram of a GPS Receiver
10kΩ
18kΩ
AD831
MIXER
CODE GENERATOR
Rev. E | Page 14 of 20
DEMODULATOR
AD630
The band-pass response is shown in Figure 41.
PLL SYNTHESIZERS AND LOOP FILTERS
Phase-lock loop filters are used in AM/FM modulation.
Loop filters in PLL design require accuracy and care in their
implementation. The AD8671/AD8672/AD8674 are ideal
candidates for such filter design; the low offset voltage and low
input bias current minimize the output error. In addition to the
excellent dc specifications, the AD8671/AD8672/AD8674 have
a unique performance at high frequencies; the high open-loop
gain and wide bandwidth allow the user to design a filter with a
high closed-loop gain if desirable. To optimize the filter design,
it is recommended to use small value resistors to minimize the
thermal noise. A simple example is shown in Figure 42.
100
LOW-PASS FILTER
DETECTOR
V
PHASE
S
AD8610
= ±15V
Figure 42. PLL Filter Simplified Block Diagram
1k
Figure 41. Band-Pass Response
CHARGE
PUMP
IN
10k
AD8369
D
VGA
Hz
100k
V
V
EE
10kΩ
CC
R1
AD10200
1nF
C1
1M
ADC
VCO
10M