LF-to-2.5GHz Dual Logarithmic Detector/

Controller for Power, Gain, and VSWR Measurements

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13

Measuring Gain

The MAX2016 can be used to measure the gain of an

RF block (or combination of blocks) through the imple-

mentation outlined in Figure 3. As shown, a coupled

signal from the input of the block is fed into RFINA,

while the coupled output is connected to RFINB. The

DC output voltage at OUTD is proportional to the power

difference (i.e., gain).

The gain of a complete receiver or transmitter lineup

can likewise be measured since the MAX2016 accepts

RF signals that range from low frequency to 2.5GHz;

see Figure 4. The MAX2016 accurately measures the

gain, regardless of the different frequencies present

within superheterodyne architectures.

For accurate measurement of signals carrying signifi-

cant amplitude modulation, limit the bandwidth of the

difference amplifier to be less than the lowest modula-

tion frequency. This will minimize the ripple in the

OUTD waveform. This is particularly appropriate if the

system-level time delay between the two sense points

is significant with respect to the period of modulation.

MAX2016

RFINA

RFINB

IN

LOGARITHMIC

DETECTOR

LOGARITHMIC

DETECTOR

GND

OUTD

SETD

20k

Ω

COUPLER

COUPLER

RF BLOCK

OUT

OUTD

Figure 3. Gain Measurement Configuration

MAX2016

LNA

RFINA

RFINB

LOGARITHMIC

DETECTOR

LOGARITHMIC

DETECTOR

COUPLER

LO

MIXER

COUPLER

OUTD

SETD

20k

Ω

OUT

Figure 4. Conversion Gain Measurement Configuration