2.4GHz Monolithic

Voltage-Controlled Oscillator for Automotive

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Detailed Description

Oscillator

The MAX2750AUA VCO is implemented as an LC oscil-

lator topology, integrating all of the tank components

on-chip. This fully monolithic approach provides an

extremely easy-to-use VCO, equivalent to a VCO mod-

ule. The frequency is controlled by a voltage applied to

the TUNE pin, which is internally connected to the var-

actor. The VCO core uses a differential topology to pro-

vide a stable frequency versus supply voltage and

improve the immunity to load variations. In addition,

there is a buffer amplifier following the oscillator core to

provide added isolation from load variations and to

boost the output power.

Output Buffer

The oscillator signal from the core drives an output

buffer amplifier. The amplifier is internally matched to

50Ω including an on-chip DC-blocking capacitor. No

external DC-blocking capacitor is required, eliminating

the need for any external components. The output

load-pulling effects. The amplifier boosts the oscillator

signal to a level suitable for driving most RF mixers.

Applications Information

Tune Input

The tuning input is typically connected to the output of the

PLL loop filter. The loop filter provides an appropriately

low-impedance source. The input may incorporate an

extra RC filter stage to reduce high-frequency noise and

spurious signals. Any excess noise on the tuning input is

directly translated into FM noise, which can degrade the

phase-noise performance of the oscillator. Therefore, it is

important to minimize the noise introduced on the tuning

input. A simple RC filter with low corner frequency is

needed during testing to filter the noise present on the

voltage source driving the tuning line.

Layout Issues

Always use controlled impedance lines (microstrip,

coplanar waveguide, etc.) for high-frequency signals.

Always place decoupling capacitors as close as possi-

sary to add additional decoupling capacitors located

further from the device. Always provide a low-induc-

tance path to ground, and keep GND vias as close as

possible to the device. Thermal reliefs on GND pads

are not recommended.

SHDN

1

2

8

7

GND

OUT

TUNE

GND

BYP

µMAX

+

TOP VIEW

3

4

6

5

MAX2750AUA

Pin Configuration