Micrel, Inc.

MAQRF112

February 7, 2013

9

Revision 1.0

FSK Operation

Figure

3

shows

the

reference

oscillator

circuit

configuration

for

FSK

operation.

To

operate

the

MAQRF112

device

in

FSK

mode,

one

additional

the

XTAL_MOD

pin.

Crystal parameters

for FSK

operation are the same as for ASK operation except:

•

When the ESR of the crystal is at 20

Ω,

•

When the ESR of the crystal is at 300

Ω,

Figure 3. Reference Oscillator FSK Operation

frequency, high-side, and low-side RF frequency. See

Figure 4.

Use Equation 3 to calculate the FSK high-side frequency

calculation.

STRAY

2

L

1

L

LOAD

C

C

1

C

1

1

C

+

+

=

Eq. 3

Use Equation 4 to calculate the FSK low-side frequency

calculation.

STRAY

FSK

2

L

1

L

LOAD

C

C

C

1

C

1

1

C

+

+

+

=

Eq. 4

Figure 4. MAQRF112 Frequency Deviation

FSK modulation is achieved by pulling the crystal at the

desired data rate. Pulling the crystal frequency is done

which pulls the reference oscillator high. A logic-level

Ω to

1000

Ω and depends on the crystal chosen. Board-level

optimization is required to optimize for frequency

deviation and occupied bandwidth requirements.