Datasheet AD8671, AD8672, AD8674 (Analog Devices) - 14

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AD8671/AD8672/AD8674 Data Sheet ADC LOW NOISE OP AMP MIXER VGA BAND-PASS FILTER DEMODULATOR LOW-PASS FILTER AD8671 AD8671 AD831 AD630 AD8610 AD8369 AD10200 CODE GENERATOR
03718-B-039 Figure 37. Simplified Block Diagram of a GPS Receiver
GPS RECEIVER
The band-pass response is shown in Figure 39. GPS receivers require low noise to minimize RF effects. The precision of the AD8671 makes it an excellent choice for such
VS = ±15V
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 37 shows a simplified block diagram of a GPS receiver. µ
V/DIV
The next section details the design equations.
200 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 38 shows a second-order band-pass KRC filter.
100 1k 10k 100k 1M 10M R3 Hz
03718-B-041
2.25k
Ω
V
Figure 39. Band-Pass Response
CC PLL SYNTHESIZERS AND LOOP FILTERS R1 C2 2.25k
Ω
1nF
Phase-lock loop filters are used in AM/FM modulation.
V C2 R2 IN 1nF 2.25k
Ω
R 18k
Ω
B
Loop filters in PLL design require accuracy and care in their implementation. The AD8671/AD8672/AD8674 are ideal
VEE
candidates for such filter design; the low offset voltage and low
R 10k
Ω
A
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 03718-B-040 gain and wide bandwidth al ow the user to design a filter with a Figure 38. Band-Pass KRC Filter high closed-loop gain if desirable. To optimize the filter design, The equal component topology yields a center frequency it is recommended to use small value resistors to minimize the thermal noise. A simple example is shown in Figure 40. fo = 2 2 RC π
R1 C1 10k
Ω
1nF VCC
and Q = 2 4 − K
PHASE CHARGE
where:
DETECTOR PUMP VCO
R
D
B K =1 + R
V
A
EE IN
03718-B-042 Figure 40. PLL Filter Simplified Block Diagram Rev. F | Page 14 of 20 Document Outline Specifications Electrical Characteristics, ±5.0 V Electrical Characteristics, ±15 V Absolute Maximum Ratings ESD Caution Typical Performance Characteristics Applications Power Dissipation Calculations Unity-Gain Follower Applications Output Phase Reversal Total Noise vs. Source Resistance Total Harmonic Distortion (THD) and Noise Driving Capacitive Loads GPS Receiver Band-Pass Filter PLL Synthesizers and Loop Filters Outline Dimensions Ordering Guide