MICRF007BM Просмотр технического описания (PDF) - Micrel

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MICRF007BM

QwikRadio® Low-Power UHF Receiver

Micrel 

MICRF007

Functional Diagram

Micrel

CAGC

CAGC

ANT

RF

Amp

VDD

VSS

f RX

fLO

fIF IF

Amp

Synthesizer

5th Order

Band-Pass Filter

430kHz

IF

Amp

AGC

Control

Peak

Detector

2nd Order

Programmable

Low-Pass Filter

Switched-

Capacitor

Resistor

RSC

Compa-

rator

UHF Downconverter

OOK Demodulator

DO

CTH

CTH

SHUT

Control

Logic

REFOSC

Cystal

or

Ceramic

Resonator

fT

MICRF007

Reference

Oscillator

Reference and Control

MICRF007 Block Diagram

Applications Information and Functional

Description

Refer to the functional diagram. Three sections of the IC are

identified: UHF Down-converter, OOK Demodulator and Ref-

erence and Control. Also shown are two capacitors (CTH,

CAGC) and one timing component (Y1), usually a crystal.

With the exception of a supply decoupling capacitor, these

are the only external components needed by the MICRF007

to assemble a complete UHF receiver.

For optimal performance, MICRF007 input impedance must

be matched to the antenna impedance. The matching network

will add an additional two or three components.

There is one control input, SHUT pin. The SHUT function is

used to enable the receiver. This input is CMOS compatible,

and is pulled-up on the IC.

Roll-off response of the IF Band-Pass Filter is 5th order, while

the demodulator data filter exhibits a 2nd order response.

The MICRF007 is a standard super-heterodyne receiver with

a narrow IF filter bandwidth of 700kHz. It is less susceptible to

interfering RF signals. The MICRF007 RF center frequency is

controlled by an integrated PLL/VCO frequency synthesizer,

which is locked to the reference oscillator frequency, typically

set by a crystal. A tight tolerance transmitter such as SAW or

crystal-based transmitters must be used for the system.

The MICRF007 has a fully integrated base-band demodulator

filter. The filter has a fixed 2.5kHz bandwidth and exhibits a

2nd order response. This filter limits the receiver raw data

rate to 3.2Kbps NRZ.

Design Steps

The following steps are the basic design steps for using

the MICRF007 receiver:

1. Select the reference oscillator

2. Select the CTH capacitor

3. Select the CAGC capacitor

Step 1: Selecting Reference Oscillator

All timing and tuning operations on the MICRF007 are de-

rived from the internal Colpitts reference oscillator. Timing

and tuning is controlled through the REFOSC pin in one of

two ways:

1. Connect a crystal.

2. Drive this pin with an external timing signal.

The specific reference frequency required is related to the

system transmit frequency.

Crystal Selection

Care should be taken to ensure low ESR crystals are se-

lected. “Application Hint 35” provides additional information

and recommended sources for crystals.

When a crystal is used, the minimum voltage is 300mVPP. If

using an externally applied signal, it should be AC-coupled

and limited to the operating range of 0.1VPP to 1.5VPP.

Selecting Reference Oscillator Frequency fT

As with any super-heterodyne receiver, the difference between

the internal local oscillator (LO) frequency fLO and

the incoming transmit frequency fTX should equal the IF

center frequency. Equation 1 may be used to compute the

M9999-021705

6

February 17, 2005

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