MICRF213 datasheet(6/16 Pages) MICREL

6 / 16 page

Micrel, Inc.

MICRF213

May 2007

M9999-052307-A

(408) 944-0800

Functional Diagram

ANT

CAGC

RSSI

CTH

SEL

VDD

Mixer

VSS

fLO

SEL

SHDN

SQUELCH

Amp

Synthesizer

Reference and Control

Control Logic

OOK

Demodulator

Control Logic

IMAGE

REJECT

FILTER

–f

Amp

Detector

AGC

RSSI

Slicing

Level

Programmable

Low Pass Filter

Control

Logic

Reference

Oscillator

RO1

RO2

Crystal

Figure 1. Simplified Block Diagram

Functional Description

Figure 1.

Simplified Block Diagram. It is the basic

structure of the MICRF213. It is made of three sub-

blocks; Image Rejection UHF Down-converter, the OOK

Demodulator,

and

Reference

and

Control

Logics.

Outside the device, the MICRF213 requires only three

components to operate; two capacitors (CTH, and

CAGC) and the reference frequency device, usually a

quartz crystal. An additional five components may be

used to improve performance. These are: power supply

decoupling capacitor, two components for the matching

network and two components for the pre-selector band

pass filter.

Receiver Operation

LNA

The RF input signal is AC-coupled into the gate circuit of

the grounded source LNA input stage. The LNA is a

Cascoded NMOS.

Mixers and Synthesizer

The LO ports of the Mixers are driven by quadrature

local oscillator outputs from the synthesizer block. The

local oscillator signal from the synthesizer is placed on

the low side of the desired RF signal. This allows

suppression of the image frequency at twice the IF

frequency below the wanted signal. The local oscillator

is set to 32 times the crystal reference frequency via a

phase-locked loop synthesizer with a fully integrated

loop filter.

Image Reject Filter and Band-Pass Filter

The IF ports of the mixer produce quadrature down

converted IF signals. These IF signals are low-pass

filtered. This removes higher frequency products prior to

the image reject filter where they are combined to reject

the image frequencies. The IF signal then passes

through a third order band pass filter. The IF center

frequency is 0.86MHz. The IF BW is 235KHz @

315MHz, this will vary with RF operating frequency. The

IF BW can be calculated via direct scaling:

BWIF = BWIF@315MHz ×

⎟

⎠

⎞

⎜

⎝

⎛

315

(MHz)

Freq

Operating

These filters are fully integrated inside the MICRF213.

After filtering, four active gain controlled amplifier stages

enhance the IF signal to proper level for demodulation.

OOK Demodulator

The demodulator section is comprised of detector,

programmable

low

pass

filter,

slicer,

and

AGC

comparator.

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