MAX2016 Просмотр технического описания (PDF) - Maxim Integrated

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MAX2016

LF-to-2.5GHz Dual Logarithmic Detector/Controller for Power, Gain, and VSWR Measurements

Maxim Integrated 

LF-to-2.5GHz Dual Logarithmic Detector/

Controller for Power, Gain, and VSWR Measurements

Power-Controller Mode

The MAX2016 can also be used as a power detector/

controller within an AGC loop. Figure 7 depicts a sce-

nario where the MAX2016 is employed as the AGC cir-

cuit. As shown in the figure, the MAX2016 monitors the

output of the PA through a directional coupler. An inter-

nal differencing amplifier (Figure 5) compares the

detected signal with a reference voltage determined by

VSET_. The differencing amplifier increases or decreas-

es the voltage at OUT_, according to how closely the

detected signal level matches the VSET_ reference. The

MAX2016 maintains the power of the PA to a level

determined by the voltage applied to SET_.

Since the logarithmic detector responds to any ampli-

tude modulation being carried by the carrier signal, it

may be necessary to insert an external lowpass filter

between the differencing amplifier output

(OUTA/OUTB) and the gain-control element to remove

this modulation signal.

POWER AMPLIFIER

TRANSMITTER

LOWPASS

FILTER

GAIN-CONTROL INPUT

COUPLER

OUTA/

OUTB

RFINA/

LOGARITHMIC RFINB

DETECTOR

SET-POINT

DAC

SETA/

SETB

20kΩ

20kΩ

MAX2016

Figure 7. In Power-Controller Mode, the DC Voltage at OUTA or

OUTB Controls the Gain of the PA, Leading to a Constant

Output Power Level (Note: Only one controller channel is

shown within the figure. Since the MAX2016 is a dual con-

troller/detector, the second channel can be easily implemented

by using the adjacent set of input and output connections.)

OUTA and OUTB Slope Adjustment

The transfer slope function of OUTA and OUTB can be

increased from its nominal value by varying resistors

R1 and R2 (see the Typical Application Circuit). The

equation controlling the slope is:

( ) SLOPE

OUTA

OR OUTB

=

⎛

⎝⎜

9

mV

dB

⎞

⎠⎟

⎡

⎢

⎣⎢

R1 or R2

20k

+ 40k ⎤

⎥

⎦⎥

OUTD Slope Adjustment

The transfer slope function of OUTD can be increased

from its nominal value by varying resistor R3 (see the

Typical Application Circuit). The equation controlling

the slope is:

SLOPE

OUTD

=

⎛

⎝⎜

−25

mV

dB

⎞

⎠⎟

⎛

⎝⎜

R3 + 20k ⎞

20k ⎠⎟

Input Highpass Filters

The MAX2016 integrates a programmable highpass fil-

ter on each RF input. The lower cutoff frequency of the

MAX2016 can be decreased by increasing the external

capacitor value between FA1 and FA2 or FB1 and FB2.

By default, with no capacitor connecting FA1 and FA2

or FB1 and FB2, the lower cutoff frequency is 20MHz.

Using the following equation determines the lowest

operating frequency:

frequency = 1

2πRC

where R = 2Ω.

Differential Output Video Filter

The bandwidth and response time difference of the out-

put amplifier can be controlled with the external capaci-

tor, C15, connected between FV1 and FV2. With no

external capacitor, the bandwidth is greater than 20MHz.

The following equation determines the bandwidth of the

amplifier difference:

frequency = 1

2πRC

where R = 1.8kΩ.

Use a video bandwidth lower than the anticipated low-

est amplitude-modulation frequency range to yield the

greatest accuracy in tracking the average carrier

power for high peak-to-average ratio waveforms.

______________________________________________________________________________________ 15

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