MAX2101CMQ Ver la hoja de datos (PDF) - Maxim Integrated

Número de pieza

componentes Descripción

Fabricante

MAX2101CMQ

6-Bit Quadrature Digitizer

Maxim Integrated 

6-Bit Quadrature Digitizer

VS

(fS = 600MHz)

RS

50Ω

(-47dBm to -7dBm)

CC

LSER

10nF

8nH

90

IFIN

CSH

1pF

MAX2101

RTERM

25Ω

CTERM

10nF

91

IFINB

Figure 14. Example of Input Network to Minimize VSWR and Noise Figure

ments were calculated assuming a 600MHz source fre-

quency. Capacitor CTERM provides an AC termination

for the complementary input IFINB. Resistor RTERM pro-

vides superior noise figure performance by optimizing

the tradeoff between thermal induced noise and the

gain of the input amplifier. This network also provides

ancillary rejection of out-of-band energy, improving the

receiver noise figure and resulting SNR. The topology

shown above produces a VSWR less than 1.7:1 over

the intended UHF band. Do not DC couple the inputs to

ground, as this would result in saturation of the input

stage.

More elaborate matching networks can be designed

depending on the need of the receiver system.

__________Applications Information

Voltage-Controlled Oscillator Equivalent

Input Network and Resonator Issues

The MAX2101 performs the quadrature demodulation

and digitizing functions within a digital receiver system.

A vital component of the quadrature detection function

is the generation of a local oscillator (LO) frequency.

This signal is typically generated by a VCO controlled

by a phase-locked loop. The VCO topology normally

used for high dynamic range receivers is the negative

resistance amplifier and resonator, due to superior

phase-noise performance. The MAX2101 provides the

negative resistance amplifier on-chip, and can be easi-

ly interfaced with an off-chip resonant network.

The MAX2101’s VCO amplifier uses a differential topol-

ogy for several reasons. The differential interface with

the resonator network provides superior rejection of

spurious signals that might otherwise add to or distort

the resulting LO. The differential interface minimizes the

effect of parasitic package-related elements that affect

the resonant frequency and the loaded Q of the net-

work. The differential-drive network minimizes second-

harmonic distortion that might create undesirable

mixing products within the signal chain.

Figure 15 shows the simplified input network of the

negative impedance amplifier, configured as a Wilson

oscillator. The amplifier is a simple differential emitter

coupled pair with emitter degeneration for controlled

open-loop gain. The positive feedback necessary to

create the negative input impedance is performed with

the feedback capacitors, CF, and the coupling capaci-

tors, CC. The capacitors ensure operation over the

intended 400MHz to 700MHz spectrum, and add mini-

mal noise to the system. RB1 provides a proper bias

voltage for the capacitors (partially constructed with

voltage-dependent pn junctions) and provides for DC

interface with a shunting resonant inductor. Note that

biasing networks are simplified for brevity.

The MAX2101’s negative impedance amplifier expects

a parallel resonant network. Figure 5 shows an example

of a tunable resonant network. The resonator is driven

from the phase-locked loop filter output, as noted. The

loaded Q of the resonant network, and to a lesser

extent the absolute values of the resonant elements,

determine the VCO’s phase-noise performance. As a

result, take care during the design of the resonator to

maximize the loaded Q. To achieve the phase-noise

18 ______________________________________________________________________________________

Share Link: