MICRF211AYQS datasheet(6/18 Pages) MICREL

6 / 18 page

Micrel

MICRF211

March 2007

M9999-030107

(408) 944-0800

Functional Diagram

Figure 1. Simplified Block Diagram.

Functional Description

Figure 1. Simplified Block Diagram that illustrates the

basic structure of the MICRF211. It is made of three

sub-blocks; Image Rejection UHF Down-converter, the

OOK Demodulator, and Reference and Control Logics.

Outside the device, the MICRF211 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 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, and this

varies with RF operating frequency. The IF BW can be

calculated via direct scaling:

BWIF = BWIF@433.92 MHz ×

⎟

⎠

⎞

⎜

⎝

⎛

433.92

(MHz)

Freq

Operating

These filters are fully integrated inside the MICRF211.

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.

Detector and Programmable Low-Pass Filter

The demodulation starts with the detector removing the

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