ADL5906SCPZN-R2 datasheet(20/32 Pages) AD

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ADL5906

Data Sheet

Rev. 0 | Page 20 of 32

BASIS FOR ERROR CALCULATIONS

The slope and intercept used in the error plots are calculated using

the coefficients of a linear regression performed on data collected

in its central operating range. The error plots in the Typical

Performance Characteristics section are shown in two formats:

error from the ideal line and error with respect to the 25°C output

voltage. The error from the ideal line is the decibel difference in

VRMS from the ideal straight-line fit of VRMS calculated by the linear

regression fit over the linear range of the detector, typically at

25°C. The error in decibels is calculated by

Error (dB) = (VRMS − Slope × (PIN − PZ))/Slope

(9)

where PZ is the x-axis intercept expressed in decibels relative to

1 mW (the input amplitude that produces a 0 V output if such an

output were possible).

The error from the ideal line is not a measure of absolute accuracy

because it is calculated using the slope and intercept of each device.

However, it verifies the linearity and the effect of temperature

and modulation on the response of the device. An example of

this type of plot is Figure 9. The slope and intercept that form

the ideal line are those at 25°C with CW modulation. Figure 4,

Figure 5, Figure 7, and Figure 8 show the error with various

popular forms of modulation with respect to the ideal CW

line. This method for calculating error is accurate, assuming

that each device is calibrated at room temperature.

In the second plot format, the VRMS voltage at a given input

amplitude and temperature is subtracted from the corresponding

VRMS at 25°C and then divided by the 25°C slope to obtain an error

in decibels. This type of plot does not provide any information

on the linear-in-dB performance of the device; it merely shows

the decibel equivalent of the deviation of VRMS over temperature,

given a calibration at 25°C. When calculating error from any

one particular calibration point, this error format is accurate. It

is accurate over the full range shown on the plot assuming that

enough calibration points are used. Figure 12 shows this plot type.

The error calculations for Figure 34 are similar to those for the

VRMS plots. The slope and intercept of the VTEMP function vs.

temperature are determined and applied as follows:

Error (°C) = (VTEMP − Slope × (Temp − TZ))/Slope

(10)

where:

VTEMP is the voltage at the TEMP pin at that temperature.

Slope is, typically, 4.8 mV/°C.

Temp is the ambient temperature of the ADL5906 in degrees

Celsius.

TZ is the x-axis intercept expressed in degrees Celsius (the

temperature that would result in a VTEMP of 0 V if this were

possible).

MEASUREMENT MODE BASIC CONNECTIONS

The basic connections circuit for ADL5906 is shown in Figure 51.

The ADL5906 requires a single supply of nominally 5 V. The

supply is connected to the VPOS1 and VPOS2 supply pins.

Decouple each of these pins using two capacitors with values equal

or similar to those shown in Figure 51. Place these capacitors as

close as possible to the VPOS pins. The three no connect pins

(NIC) are not internally connected. Leave these pins unconnected.

An external 60.4 Ω resistor combines with the relatively high RF

input impedance of the ADL5906 to provide a broadband 50 Ω

match. Place an ac coupling capacitor between this resistor and

RFIN+. AC-couple the RFIN− input to ground using the same

value capacitor. To operate down to 10 MHz, the coupling

capacitors must be at least 100 pF.

The ADL5906 is placed in measurement mode by connecting

the VRMS pin to the VSET pin. In measurement mode, the output

voltage is proportional to the log of the rms input signal level.

SETTING VTADJ

As described in the Theory of Operation section, the output

temperature drift can be compensated by applying a voltage to

the TADJ pin. The compensating voltage varies with frequency.

The voltage for the TADJ pin can be easily derived from a resistor

divider connected to the VREF pin. Table 4 shows the recommended

VTADJ voltages for operation from −55°C to +125°C, along with

resistor divider values. Resistor values are chosen so that they

neither pull too much current from the VREF pin (IOUTMAX = 4 mA)

nor are so large that the maximum bias current at a VTADJ = 1 V

(14 µA) affects the resulting voltage.

The VTADJ function provides temperature compensation of

the output slope of the ADL5906. The Using VTEMP to Improve

Intercept Temperature Drift section describes how the

temperature stability of the ADL5906 can be further improved.

Table 4. Recommended VTADJ Voltages

Frequency

VTADJ (V)

R9 (Ω)

R12 (Ω)

10 MHz to 2.14 GHz

0.35

1500

270

2.6 GHz

0.4

1500

316

3.5 GHz

0.45

1500

365

5.8 GHz

1.0

1540

1200

8 GHz

1.0

1540

1200

10 GHz

1.0

1540

1200

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