MICRF213 datasheet(10/16 Pages) MICREL

10 / 16 page

Micrel, Inc.

MICRF213

May 2007

M9999-052307-A

(408) 944-0800

the top layer close to the REFOSC pins RO1 and

RO2. When care is not taken in the layout, and

crystals from other vendors are used, the oscillator

may take longer times to start as well as the time to

good data in the DO pin to show up. In some cases, if

the stray capacitance is too high (>20pF), the

oscillator may not start at all.

The crystal frequency is calculated by REFOSC = RF

Carrier/(32+(1.1/12)). The local oscillator is low side

injection (32 × 9.81563MHz = 314.1MHz), that is, its

frequency is below the RF carrier frequency and the

image frequency is below the LO frequency. Refer to

Figure 6. The product of the incoming RF signal and

local oscillator signal will yield the IF frequency, which

will then be demodulated by the detector of the

device.

fLO

f (MHz)

Image

Frequency

Desired

Signal

Figure 6. Low Side Injection Local Oscillator

REFOSC

(MHz)

Carrier

(MHz)

HIB Part Number

9.467411

303.825

SA-9.467411-F-10-H-30-30-X

9.81563

315

SA-9.815630-F-10-H-30-30-X

10.75045

345.0

SA-10.750450-F-10-H-30-30-X

Table 5. Crystal Frequency and Vendor Part Number

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. Reference the

example of the data profile, in the Figure 7, below:

Figure 7. Example of a Data Profile

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

the

demodulator

bandwidth

calculation.

The

calculation 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 140µsec, 50% duty cycle, then the pulse width will

be 70µsec (PW = (140 µsec * 50%) / 100). So, a

bandwidth of 9.286kHz would be necessary (0.65 /

70µsec). However, if this data stream had a pulse

period with a 20% duty cycle, then the bandwidth

required would be 23.2kHz (0.65 / 28µsec), 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

(usec)

Maximum

baud rate for

50% Duty

Cycle (hertz)

Short

1180

551

908

Open

Short

2360

275

1815

Short

Open

4720

138

3631

Open

9400

7230

Table 6. JP1 and JP2 Setting, 315MHz

Capacitors C6 and C4, Cth and Cagc capacitors

respectively, provide the 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 not a preamble. See Figure 7 for an

example of a data profile.

Other frequencies will have different demodulator

bandwidth limits, which are derived from the reference

oscillator frequency. Table 7 and Table 8, below,

show

the limits

for the

other two

most

used

frequencies.

SEL0

JP1

SEL1

JP2

Demod.

(hertz)

Shortest

Pulse

(usec)

Maximum

baud rate for

50% Duty

Cycle (hertz)

Short

1140

570

8770

Open

Short

2280

285

1754

Short

Open

4550

143

3500

Open

9100

7000

Table 7. JP1 and JP2 Setting, 303.825MHz

SEL0

JP1

SEL1

JP2

Demod.

(hertz)

Shortest

Pulse

(usec)

Maximum

baud rate for

50% Duty

Cycle (Hertz)

Short

1290

504

992

Open

Short

2580

252

1985

Short

Open

5170

126

3977

Open

10340

7954

Table 8. JP1 and JP2 Setting, 345.0MHz

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