MLX71120

300 to 930MHz

FSK/FM/ASK Receiver

REVISION 009 - JUNE 16, 2017

3901071120

1.6. Mixer Section

The mixer section consists of two mixers. Both are double-balanced mixers. The second mixer is built as an image

rejection mixer. The first mixer’s inputs (MIXP and MIXN) are functionally the same. For single-ended drive, the

unused input has to be tied to ground via a capacitor. A soft band-pass filter is placed between the mixers.

RFSEL

Description

0

Input frequency range 300 to 470MHz

1

Input frequency range 610 to 930MHz

Pin RFSEL is used to select the required RF band. The LO frequencies and the proper sidebands for image suppression

will be set accordingly. The mixer output (MIXO) is to drive an external IF filter. This output is set up by a source

follower that can be biased to create a driving impedance of either 1500 Ohms or 330 Ohms, depending on the logic

level at pin IFSEL.

IFSEL

Description

0

IF2 = 455 kHz

1

IF2 = 10.7 MHz

This feature allows to use standard ceramic filters for 455kHz and 10.7MHz. They can be connected directly without

additional matching elements. The overall voltage conversion gain of the mixer section is approximately 25dB.

1.7. IF Amplifier

After having passed the IF filter, the signal is amplified by a high-gain limiting amplifier. It consists of several AC-

coupled gain stages with a bandwidth of 400kHz to 11MHz. The overall small-signal pass-band gain is about 80dB. A

received-signal-strength indicator (RSSI) signal is generated within the IF amplifier and is available at pin RSSI.

1.8. PLL Synthesizer

The PLL synthesizer consists of a fully integrated voltage-controlled oscillator running at 400MHz to 640MHz, a

distributed feedback divider chain, an edge-triggered phase-frequency detector, a charge pump, a loop filter and a

crystal-based reference oscillator. The PLL is used for generating the LO signals. The LO1 is directly taken from the VCO

output, and the LO2 is derived from the LO1 signal passing the N1 counter. Another counter N2 follows N1. The

can be chosen via pin RFSEL.

RFSEL

0

400

640

100

160

4

6

24

1

400

640

200

320

2

12

24