MAX7036(2010) 查看數據表（PDF） - Maxim Integrated

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MAX7036
(Rev.:2010)

300MHz to 450MHz ASK Receiver with Internal IF Filter

Maxim Integrated 

300MHz to 450MHz ASK Receiver

with Internal IF Filter

For example, to choose a Butterworth filter response

with a corner frequency of 6kHz:

C5

=

1.000

(1.414)(100kΩ)(3.14)(6kHz)

=

375pF

C6

=

1.414

(4)(100kΩ)(3.14)(6kHz)

=

186pF

Choosing standard capacitor values changes C5 to

390pF and C6 to 180pF, as shown in the Typical

Application Circuit.

Table 1. Coefficients to Calculate C5

and C6

FILTER TYPE

a

b

Butterworth (Q = 0.707)

1.414

1.000

Bessel (Q = 0.577)

1.3617

0.618

MAX7036 RSSI

RDF2

100kΩ

RDF1

100kΩ

16

14

15

DSP

OPP

DFFB

C6

C5

Figure 2. Sallen-Key Lowpass Data Filter

Data Slicer

The data slicer takes the analog output of the data filter

and converts it to a digital signal. This is achieved by

using a comparator and comparing the analog input to

a threshold voltage. One input is supplied by the data-

filter output. Both comparator inputs are accessible off

chip to allow for different methods of generating the

slicing threshold, which is applied to the second com-

parator input.

The suggested data-slicer configuration uses a resistor

(R1) connected between DSN and DSP with a capaci-

tor (C4) from DSN to GND (Figure 3). This configuration

averages the analog output of the filter and sets the

threshold to approximately 50% of that amplitude. With

this configuration, the threshold automatically adjusts

as the analog signal varies, minimizing the possibility

for errors in the digital data. The values of R1 and C4

affect how fast the threshold tracks to the analog ampli-

tude. Be sure to keep the corner frequency of the RC

circuit much lower than the lowest expected data rate.

MAX7036

DATA

SLICER

20

DATAOUT

DATA

FILTER

17

16

DSN

DSP

R1

C4

Figure 3. Generating Data-Slicer Threshold

Note that a long string of zeros or ones can cause the

threshold to drift. This configuration works best if a

coding scheme (e.g., Manchester coding, which has an

equal number of zeros and ones) is used.

Peak Detector

The peak-detector output (PDOUT), in conjunction with

an external RC filter, creates a DC output voltage equal

to the peak value of the data signal. The resistor pro-

vides a path for the capacitor to discharge, allowing the

peak detector to dynamically follow peak changes of

the data-filter output voltage. The peak detector can be

used for at least two functions. First, it can serve as an

RSSI for ASK modulation. Second, it can be used for

faster data-slicer response by adding it to the threshold

pin (DSN) on the data-slicer comparator (Figure 4). The

two capacitors in this circuit should be equal, and the

peak detector resistor should be approximately 10

10 ______________________________________________________________________________________

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