MICRF219 データシートの表示（PDF） - Micrel

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MICRF219

300MHz to 450MHz ASK Receiver with RSSI, Auto-Poll, Bit-Check and Squelch

Micrel 

Micrel

MICRF219

Functional Description

The simplified block diagram, shown in Figure 1,

illustrates the basic structure of the MICRF219 receiver.

It is made up of four sub-blocks:

• UHF Down-converter

• OOK Demodulator

• Reference and Control logic

• Auto-poll circuitry

Outside the device, the MICRF219 receiver requires just

three components to operate: two capacitors (CTH, and

CAGC) and the reference frequency device (usually a

quartz crystal). An additional five components are used

to improve performance; a power supply decoupling

capacitor, two components for the matching network,

and two components for the pre-selector band-pass

filter.

Receiver Operation

UHF Downconverter

The UHF down-converter has six components: LNA,

mixers, synthesizer, image reject filter, band pass filter

and IF amp.

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 amplifier. The amplified RF signal is

then fed to the RF ports of two double balanced mixers.

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 to allow

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 to remove 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

1.2MHz. The IF BW is 330kHz @ 433.92MHz. This

varies with RF operating frequency.

The IF BW can be calculated via direct scaling:

BWIF = BWIF@433.92 MHz ×

⎜⎛ Operating Freq (MHz) ⎟⎞

⎝

433.92

⎠

These filters are fully integrated inside the MICRF219.

After filtering, four active gain controlled amplifier stages

enhance the IF signal to its proper level for

demodulation.

OOK Demodulator

The demodulator section is comprised of detector,

programmable low pass filter, slicer, and AGC

comparator.

Detector and Programmable Low-Pass Filter

The demodulation starts with the detector removing the

carrier from the IF signal. Post detection, the signal

becomes base band information. The programmable

low-pass filter further enhances the baseband

information. There are four programmable low-pass

filter BW settings: 1625Hz, 3250Hz, 6500Hz, 13000Hz

for 433.92MHz operation. Low pass filter BW will vary

with RF Operating Frequency. Filter BW values can be

easily calculated by direct scaling. See equation below

for filter BW calculation:

BWOperating Freq = BW@433.92MHz*

⎜⎛ Operating Freq (MHz) ⎟⎞

⎝

433.92

⎠

It is very important to choose filter setting that fits best

the intended data rate to minimize data distortion.

Demod BW is set at 13000Hz @ 433.92MHz as default

(assuming both SEL0 and SEL1 pins are floating). The

low pass filter can be hardware set by external pins

SEL0 and SEL1.

SEL0

0

1

0

1

SEL1

0

0

1

1

Demod BW (@ 434MHz)

1625Hz

3250Hz

6500Hz

13000Hz - default

Table 1. Demodulation BW Selection

June 2011

7

M9999-060811

(408) 944-0800

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