MICRF211 Ver la hoja de datos (PDF) - Micrel

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Fabricante

MICRF211

3V, QwikRadio® 433.92 MHz Receiver

Micrel 

Micrel

MICRF211

JP1 and JP2 are the bandwidth selection for the

demodulator bandwidth. To set it correctly, it is

necessary to know the shortest pulse width of the

encoded data sent in the transmitter. Like in the

example of the data profile in the figure 7 below, PW2

is shorter than PW1, so PW2 should be used for the

demodulator bandwidth calculation which is found by

0.65/shortest pulse width. After this value is found, the

setting should be done according to Table 6. For

example, if the pulse period is 100µsec, 50% duty

cycle, the pulse width will be 50µsec (PW = (100µsec

× 50%) / 100). So, a bandwidth of 13kHz would be

necessary (0.65 / 50µsec). However, if this data

stream had a pulse period with 20% duty cycle, the

bandwidth required would be 32.5kHz (0.65 / 20µsec),

which exceeds the maximum bandwidth of the

demodulator circuit. If one tries to exceed the

maximum bandwidth, the pulse would appear

stretched or wider.

SEL0

JP1

Short

Open

Short

Open

SEL1

JP2

Short

Short

Open

Open

Demod.

BW

(hertz)

1625

3250

6500

13000

Shortest

Pulse

(µsec)

400

200

100

50

Maximum

baud rate for

50% Duty

Cycle (hertz)

1250

2500

5000

10000

Table 6. JP1 and JP2 setting, 433.92 MHz.

Other frequencies will have different demodulator

bandwidth limits, which are derived from the reference

oscillator frequency. Table 7 and Table 8 below shows

the limits for the other two most used frequencies.

SEL0

JP1

Short

Open

Short

Open

SEL1

JP2

Short

Short

Open

Open

Demod.

BW

(hertz)

1565

3130

6261

12523

Shortest

Pulse

(µsec)

416

208

104

52

Maximum

baud rate for

50% Duty

Cycle (hertz)

1204

2408

4816

9633

Table 7. JP1 and JP2 setting, 418.0 MHz.

SEL0

JP1

Short

Open

Short

Open

SEL1

JP2

Short

Short

Open

Open

Demod.

BW

(hertz)

1460

2921

5842

11684

Shortest

Pulse

(µsec)

445

223

111

56

Maximum

baud rate for

50% Duty

Cycle (Hertz)

1123

2246

4493

8987

Table 8. JP1 and JP2 setting, 390.0 MHz.

Capacitors C6 and C4, CTH and CAGC respectively

provide time base reference for the data pattern

received. These capacitors are selected according to

data profile, pulse duty cycle, dead time between two

received data packets, and if the data pattern has or

does not have a preamble. See Figure 7, example of

a data profile.

Figure 7. Example of a Data Profile.

For best results the capacitors should always be

optimized for the data pattern used. As the baud rate

increases, the capacitor values decrease. Table 9

shows suggested values for Manchester Encoded

data, 50% duty cycle.

SEL0

JP1

Short

Open

Short

Open

SEL1

JP2

Short

Short

Open

Open

Demod.

BW

(hertz)

1625

3250

6500

13000

Cth

100nF

47nF

22nF

10nF

Cagc

4.7µF

2.2µF

1µF

0.47µF

Table 9. Suggested CTH and CAGC Values.

JP3 is a jumper used to configure the digital squelch

function. When it is high, there is no squelch applied

to the digital circuits and the DO (data out) pin has a

hash signal. When the pin is low, the DO pin activity is

March 2007

11

M9999-030107

(408) 944-0800

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