Micrel, Inc.

MICRF112

December 2011

12

M9999-120911

(408) 944-0800

Functional Diagram

Figure 3. Functional Block Diagram MICRF112 10 Pin ASK / FSK Version

Functional Description

Figure 3 shows a functional block diagram of the

MICRF112 transmitter. The MICRF112 can be best

described as a phase locked transmitter. The system

can be partitioned into six functional blocks; crystal

oscillator, PLL×32, power amplifier, enable control,

under voltage detect and open drain switch for FSK

operation.

Crystal Oscillator

The

reference

oscillator

is

crystal-based

Pierce

configuration. It is designed to accept crystals with

frequency from 9.375MHz to 14.0625MHz.

Crystal Oscillator Parameters for ASK Operation

Figure

4

shows

a

reference

oscillator

circuit

configuration for ASK operation. The reference oscillator

is capable of driving crystals with ESR range from 20Ω

to 300Ω.

When the ESR of crystal is at 20Ω, the crystal parameter

limits are:

ESR 20Ω

Figure 4. Reference Oscillator ASK Operation

When the ESR of crystal is at 300Ω, the crystal

parameter limits are:

ESR

300Ω

2 to 5pF

10 to 40fF

10 to 30pF