MAX9930 데이터 시트보기 (PDF) - Maxim Integrated

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MAX9930

2MHz to 1.6GHz 45dB RF-Detecting Controllers and RF Detector

Maxim Integrated 

2MHz to 1.6GHz 45dB RF-Detecting

Controllers and RF Detector

Filter Capacitor and Transient Response

In general, for the MAX9930/MAX9931/MAX9932, the

choice of filter capacitor only partially determines the

time-domain response of a PA control loop. However,

some simple conventions can be applied to affect tran-

sient response. A large filter capacitor, CCLPF, domi-

nates time-domain response, but the loop bandwidth

remains a factor of the PA gain-control range. The

bandwidth is maximized at power outputs near the cen-

ter of the PA’s range, and minimized at the low and

high power levels, where the slope of the gain-control

curve is lowest.

A smaller valued CCLPF results in an increased loop

bandwidth inversely proportional to the capacitor value.

Inherent phase lag in the PA’s control path, usually

caused by parasitics at OUT, ultimately results in the

addition of complex poles in the AC loop equation. To

avoid this secondary effect, experimentally determine

the lowest usable CCLPF for the power amplifier of inter-

est. This requires full consideration to the intricacies of

the PA control function. The worst-case condition,

where the PA output is smallest (gain function is steep-

est) should be used because the PA control function is

typically nonlinear. An additional zero can be added to

improve loop dynamics by placing a resistor in series

with CCLPF. See Figure 4 for the gain and phase

response for different CCLPF values.

Additional Input Coupling

There are three common methods for input coupling:

broadband resistive, narrowband reactive, and series

attenuation. A broadband resistive match is implement-

ed by connecting a resistor to ground at the external

AC-coupling capacitor at RFIN as shown in Figure 5. A

50Ω resistor (use other values for different input imped-

ances) in this configuration, in parallel with the input

impedance of the MAX9930–MAX9933, presents an

input impedance of approximately 50Ω. These devices

require an additional external coupling capacitor in

series with the RF input. As the operating frequency

increases over 2GHz, input impedance is reduced,

resulting in the need for a larger-valued shunt resistor.

Use a Smith Chart for calculating the ideal shunt resis-

tor value. Refer to the MAX4000/MAX4001/MAX4002

data sheet for narrowband reactive and series attenua-

tion input coupling.

50Ω SOURCE

50Ω

CC

RFIN

RS

50Ω

MAX9930

MAX9931

MAX9932

MAX9933

CIN

RIN

VCC

Figure 5. Broadband Resistive Matching

GAIN AND PHASE vs. FREQUENCY

80

180 MAX9930 fig04

60 GAIN

CCLPF = 2000pF

135

40

20 CCLPF = 200pF

90

CCLPF = 200pF 45

0

0

-20

-45

-40

-90

CCLPF = 2000pF

-60

-135

-80

-180

PHASE

-100

-225

10 100 1k 10k 100k 1M 10M 100M

FREQUENCY (Hz)

Figure 4. Gain and Phase vs. Frequency

SMALL-SIGNAL BANDWIDTH vs. CCLPF

10

1

0.1

0.01

100

1000

10,000

CCLPF (pF)

100,000

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