MAX7031 查看數據表（PDF） - Maxim Integrated

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MAX7031

Low-Cost, 308MHz, 315MHz, and 433.92MHz FSK Transceiver with Fractional-N PLL

Maxim Integrated 

Low-Cost, 308MHz, 315MHz, and 433.92MHz

FSK Transceiver with Fractional-N PLL

MAX7031

DATA

SLICER

DATA

DS-

DS+

R

C

MAX7031

PEAK

PEAK

DATA

DET

DET

SLICER

DATA

PDMAX

PDMIN

R

R

C

C

Figure 3. Generating Data Slicer Threshold Using a Lowpass

Filter

generates a 100mVP-P signal on the control line. This

control voltage is then filtered and sliced by the base-

band circuitry.

The FSK demodulator PLL requires calibration to over-

come variations in process, voltage, and temperature.

This is done by cycling the ENABLE pin when the

AUTOCAL pin is a logic 1. If the AUTOCAL pin is a

logic 0, calibration cannot occur.

Data Filter

The data filter for the demodulated data is implemented

as a 2nd-order, lowpass Sallen-Key filter. The pole

locations are set by the combination of two on-chip

resistors and two external capacitors. Adjusting the

value of the external capacitors changes the corner fre-

quency to optimize for different data rates. Set the cor-

ner frequency in kHz to approximately 2 times the

fastest expected Manchester data rate in kbps from the

transmitter (1.0 times the fastest expected NRZ data

rate). Keeping the corner frequency near the data rate

rejects any noise at higher frequencies, resulting in an

increase in receiver sensitivity.

The configuration shown in Figure 2 can create a

Butterworth or Bessel response. The Butterworth filter

offers a very-flat-amplitude response in the passband

Table 2. Coefficients to Calculate CF1

and CF2

FILTER TYPE

Butterworth

(Q = 0.707)

Bessel

(Q = 0.577)

a

1.414

1.3617

b

1.000

0.618

Figure 4. Generating Data Slicer Threshold Using the Peak

Detectors

and a rolloff rate of 40dB/decade for the two-pole filter.

The Bessel filter has a linear phase response, which

works well for filtering digital data. To calculate the

value of the capacitors, use the following equations,

along with the coefficients in Table 2:

CF1

=

b

a(100kΩ)(π)(fc)

CF2

=

a

4(100kΩ)(π)(fc)

where fC is the desired 3dB corner frequency.

For example, choose a Butterworth filter response with

a corner frequency of 5kHz:

CF1

=

1.000

(1.414)(100kΩ)(3.14)(5kHz)

≈

450pF

CF2

=

1.414

(4)(100kΩ)(3.14)(5kHz)

≈

225pF

Choosing standard capacitor values changes CF1 to

470pF and CF2 to 220pF. In the Typical Application

Circuit, CF1 and CF2 are named C16 and C17,

respectively.

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