AD8672ARMZ datasheet(14/20 Pages) AD

14 / 20 page

AD8671/AD8672/AD8674

Data Sheet

Rev. F | Page 14 of 20

AD8671

BAND-PASS FILTER

LOW NOISE OP AMP

MIXER

DEMODULATOR

LOW-PASS FILTER

VGA

ADC

AD10200

AD831

AD8671

AD630

AD8610

AD8369

CODE GENERATOR

Figure 37. Simplified Block Diagram of a GPS Receiver

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 37 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 38 shows a second-order band-pass KRC filter.

18k

Ω

10k

Ω

2.25k

Ω

VCC

VEE

2.25k

Ω

2.25k

Ω

1nF

VIN

1nF

Figure 38. Band-Pass KRC Filter

The equal component topology yields a center frequency

and

−

where:

The band-pass response is shown in Figure 39.

100k

100

10k

10M

VS = ±15V

Figure 39. Band-Pass Response

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 40.

10k

Ω

VCC

VEE

1nF

VCO

CHARGE

PUMP

PHASE

DETECTOR

Figure 40. PLL Filter Simplified Block Diagram

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