MAX2741(2005) データシートの表示（PDF） - Maxim Integrated

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MAX2741
(Rev.:2005)

Integrated L1-Band GPS Receiver

Maxim Integrated 

Integrated L1-Band GPS Receiver

Table 7. Detailed Register Definition for Read Address 0111: STATUS

DATA BIT

D15–D10

D9

D8

D7

D6

D5

D4

D3–D0

DEFAULT

XXXXXX Reserved

DESCRIPTION

X

Out-of-Lock (High Frequency): 1 = PLL is out of lock, VCO free-running at its highest frequency,

0 = Locked.

X

1

X

X

X

XXXX

Out-of-Lock (Low Frequency): 1 = PLL is out of lock, VCO free-running at its lowest frequency,

0 = Locked high.

XTAL Clock Selected: 1 = Synthesized 16.8MHz reference, 0 = External clock.

Parity: 1 = Even, 0 = Odd.

Reserved

LPF Autotune End: 0 = Autotune run ended; 1 = Calibrating or manual tuning.

LPF Autotune: 0000 ~ 7.7MHz; 1111 = 2.9MHz.

Applications Information

Fundamentally, the only application areas that require

careful consideration are the LNA input match and the

1st IF filter. Of course, proper supply bypassing,

grounding, and layout is required for reliable perfor-

mance from any RF circuit.

LNA Input Matching

Input matching is critical for optimum noise figure and

system sensitivity. Optimum source impedance (as seen

from the LNA input) for lowest noise figure is 29Ω + j47Ω.

Remember that optimum noise match and optimum gain

match (return loss) do not occur simultaneously, so a

good application circuit will sacrifice gain slightly in favor

of reduced noise figure. Gain and noise circles are pro-

vided in Figure 3; S11 tabular data is provided in Table 8.

G = Gmax - 1dB

NF = NFmin + 0.2dB

Table 8. MAX2741 S11

FREQ (MHz)

1100

1200

1300

1400

1500

1550

1560

1570

1575

1580

1590

1600

1650

1700

1800

1900

2000

S11 (MAG)

0.874

0.867

0.859

0.842

0.821

0.809

0.806

0.804

0.803

0.801

0.799

0.796

0.783

0.768

0.739

0.708

0.677

S11 (°)

-50.9

-56.1

-61.5

-66.9

-72.3

-74.9

-75.4

-75.9

-76.2

-76.4

-77.0

-77.5

-80.0

-82.5

-87.4

-92.3

-96.8

1st IF Interface and Filtering

The typical application uses a 37.38MHz 1st IF, and

employs an IF filter. The order of the filter should be tai-

lored to suit the application—stand-alone GPS

receivers will not require the channel-selection and

stopband attenuation of GPS receivers that are inte-

grated into other wireless handsets. Be sure that the fil-

ter topology provides DC-blocking for the IF I/O ports.

Figure 3. Gain and Noise Circles for MAX2741 LNA Input

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