Data Sheet

AD8318

USING THE AD8318

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Rev. E | 17 of 24

VARIATION IN TEMPERATURE DRIFT FROM

DEVICE TO DEVICE

Figure 36 shows a plot of output voltage and error for multiple

AD8318 devices measured at 5.8 GHz. The concentration of black

error plots represents the performance of the population at 25°C

(slope and intercept are calculated for each device). The red and

blue curves indicate the measured behavior of a population of

devices over temperature. This suggests a range on the drift (from

device to device) of 1.2 dB.

Figure 36. Output Voltage and Error vs. Temperature (+25°C, −40°C, and

+85°C) of a Population of Devices Measured at 5.8 GHz

TEMPERATURE DRIFT AT DIFFERENT

TEMPERATURES

Figure 37 shows the log slope and error over temperature for a 5.8

GHz input signal. Error due to drift over temperature consistently re-

mains within ±0.5 dB, and only begins to exceed this limit when the

ambient temperature drops below −20°C. When using a reduced

temperature range, higher measurement accuracy is achievable for

all frequencies.

Figure 37. Typical Drift at 5.8 GHz for Various Temperatures

SETTING THE OUTPUT SLOPE IN

MEASUREMENT MODE

To operate in measurement mode, VOUT is connected to VSET.

This yields the typical logarithmic slope of −25 mV/dB. The output

swing corresponding to the specified input range is then approxi-

mately 0.5 V to 2.1 V. The slope and output swing can be increased

by placing a resistor divider between VOUT and VSET (that is,

one resistor from VOUT to VSET and one resistor from VSET to

common).

As an example, if two equal resistors, such as 10 kΩ/10 kΩ, are

used, the slope doubles to approximately −50 mV/dB. The input

impedance of VSET is approximately 500 kΩ. Keep slope setting

resistors below ~50 kΩ to prevent this input impedance from affect-

ing the resulting slope. When increasing the slope, the new output

voltage range cannot exceed the output voltage swing capability

of the output stage. Refer to the Measurement Mode section for

further details.

Figure 38. Increasing the Slope