Micrel

MICRF009

January 18, 2005

6

M9999-011805

(408) 955-1690

Functional Diagram

Figure 1. MICRF009 Block Diagram

Application Information and Function

Description

Refer to “MICRF009 Block Diagram.” Identified in the block

diagram are the three sections of the IC: 1) UHF

Downconverter, 2) OOK Demodulator, 3) Reference and

crystal or ceramic resonator. With the exception of a supply

decoupling capacitor and antenna impedance matching

network, these are the only external components needed

by the MICRF009 to assemble a complete UHF receiver.

For optimal performance it is highly recommended that the

MICRF009 is impedance-matched to the antenna. The

matching network will add additional two or three

components.

Four control inputs are shown in the block diagram: SEL0,

SEL1, SWEN, and SHUT. Using these logic inputs, the

user can control the operating mode and selectable

features of the IC. These inputs are CMOS compatible and

are internally pulled-up. The IF Bandpass Filter Roll-off

response of the IF Filter is 5th order, while the demodulator

data filter exhibits a 2nd order response.

Design Steps

The following steps are the basic design steps for using the

MICRF009 receiver:

1. Select the operating mode (sweep or fixed)

2. Select the reference oscillator

3. Select the demodulator filter bandwidth

4. Select the CTH capacitor

5. Select the CAGC capacitor

Step 1: Selecting The Operating Mode

Fixed-Mode Operation

For applications where the transmit frequency is set

accurately (that is, applications where a SAW or crystal-

based transmitter is used), the MICRF009 may be

configured as a standard superheterodyne receiver (fixed-

mode). In fixed-mode operation, the RF bandwidth is

narrower making the receiver less susceptible to interfering

signals. Fixed-mode is selected by connecting SWEN to

ground.

Sweep-Mode Operation

When used in conjunction with low-cost LC transmitters,

the MICRF009 should be configured in sweep-mode. In

sweep-mode, while the topology is still superheterodynes,

the local oscillator (LO) is swept over a range of

frequencies at rates greater than the data rate. This

technique effectively increases the RF bandwidth of the