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

RI

Q3

VCC

RI

Q4

IFIN

(PIN 90)

LBW

CPAD

RF

Q1

RE

Q2

RE

RF

LBW

CPAD

IFINB

(PIN 91)

Figure 12. Equivalent Input Network

At frequencies of interest, CPAD will add a small phase

error to the impedance term. The inductance LBW mod-

els the bond wire and lead frame in series with the

input amplifier. This inductor represents a significant

portion of the input impedance, and will contribute the

majority of the variation in input impedance as the input

frequency is swept from 400MHz to 700MHz. These

variables combine to produce an actual input imped-

ance versus frequency (Figure 13).

As a result, it is challenging to achieve an extremely low

VSWR for the input of a monolithic amplifier, especially

over a wide range of frequencies. The MAX2101 provides

a VSWR less than 2:1, and delivers this performance over

the wide range of anticipated IFs currently considered.

Fortunately, for DBS, TVRO, and related applications, the

UHF IF is relatively narrow band, allowing the use of stan-

dard techniques for narrow-band impedance matching.

Narrow-Band Match

Many references cover narrow-band matching tech-

niques. The match network synthesis is simplified by

assuming the impedance of the source driving the

MAX2101’s IFIN port is positive, real, and equal to 50Ω.

For a given IF, you can simply use a Smith chart to

“map” an impedance to the intended source resis-

tance. Using a two-element matching network, you can

choose the element next to the input (CSH in Figure 14)

to translate the real portion of the impedance to match

the source resistance. The second element (LSER in

Figure 14) cancels the reactive component of the net-

work (including the effect of CSH), resulting in a real,

matched input impedance that provides maximum

IFIN (PIN 90) INPUT IMPEDENCE vs.

FREQUENCY

80

60

RE (ZIN)

40

20

0

-20

IM (ZIN)

-40

200 300 400 500 600 700 800 900

FREQUENCY (MHz)

TA = +25°C

VCC = 5V

RS = 50Ω

IFINB (PIN 91) AC TERMINATED IN 25Ω

Figure 13. Typical MAX2101 IFIN ZIN vs. Frequency (Zs = 50)

power transfer. The transformation uses only reactive

elements so that no additional resistive thermal noise is

added, which would degrade the noise figure.

Figure 14 shows the resulting impedance matching net-

work. The incident signal is AC coupled by CC. LSER

and CSH are the matching elements. CSH includes

board layout capacitance. The values of these ele-

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