MICRF211 datasheet(11/18 Pages) MICREL

11 / 18 page

Micrel

MICRF211

March 2007

M9999-030107

(408) 944-0800

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

SEL1

JP2

Demod.

(hertz)

Shortest

Pulse

(µsec)

Maximum

baud rate for

50% Duty

Cycle (hertz)

Short

1625

400

1250

Open

Short

3250

200

2500

Short

Open

6500

100

5000

Open

13000

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

SEL1

JP2

Demod.

(hertz)

Shortest

Pulse

(µsec)

Maximum

baud rate for

50% Duty

Cycle (hertz)

Short

1565

416

1204

Open

Short

3130

208

2408

Short

Open

6261

104

4816

Open

12523

9633

Table 7. JP1 and JP2 setting, 418.0 MHz.

SEL0

JP1

SEL1

JP2

Demod.

(hertz)

Shortest

Pulse

(µsec)

Maximum

baud rate for

50% Duty

Cycle (Hertz)

Short

1460

445

1123

Open

Short

2921

223

2246

Short

Open

5842

111

4493

Open

11684

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

SEL1

JP2

Demod.

(hertz)

Cth

Cagc

Short

1625

100nF

4.7µF

Open

Short

3250

47nF

2.2µF

Short

Open

6500

22nF

1µF

Open

13000

10nF

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

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