ADL5906ACPZN-R7 datasheet(23/32 Pages) AD

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Data Sheet

ADL5906

Rev. 0 | Page 23 of 32

To scale this voltage upward, choose a value for R2 and calculate

R6 using the following equation:













−

)

(

RMS

(12)

where:

RIN is the input resistance of VSET (72 kΩ).

V'RMS is the desired maximum output voltage.

VRMS is the nominal maximum output voltage before scaling

(see Figure 9 through Figure 26).

When choosing R1, R2, R6, and R15, notice the current drive

capability of the VRMS pin and the input resistance of the VSET

pin. The choice of resistors must not be too small because this

results in excessive current drawn out of the VRMS pin (the VRMS

pin can source a maximum current of 10 mA). However, choosing

an R2 that is too large is also problematic. If the value of R2 chosen

is compatible with the input resistance of the VSET pin (72 kΩ),

this input resistance, which varies slightly from part to part,

contributes to the resulting slope and output voltage. In general,

ensure that the value of R2 is at least 10 times smaller than the

input resistance of VSET. Therefore, the values for R6 and R2

must be in the 1 kΩ to 5 kΩ range. Similar values must be used

for R1 and R15.

It is also important to take into account part-to-part and frequency

variation in output swing along with the maximum output voltage

(3.9 V) of the output stage of the ADL5906. The VRMS part-to-

part distribution is well characterized at major frequency bands

in the Typical Performance Characteristics section (see Figure 12

through Figure 14, Figure 18 through Figure 20, Figure 24, and

Figure 25). The resistor values in Table 6, which were calculated

based on 3.5 GHz operation, have been conservatively chosen so

that there is no chance that the desired output voltage swings

exceed the output swing of the ADL5906 (when scaling upward)

or the input range of a 0 V to 2.5 V ADC (when scaling down-

ward). In each case, the nominal maximum voltage that results is

100 mV below the desired maximum to account for part-to-part

variation and resistor tolerances.

Table 6. Output Voltage Range Scaling Examples at 3.5 GHz

Desired Input Range (dBm)

Slope Increase

Slope Decrease

New Slope (mV/dB)

Nominal Maximum Output Voltage (V)

R6 (Ω)

R2 (Ω)

R1 (Ω)

R15(Ω)

0 to −60

274

2000

3.8

−10 to −50

681

2000

3.8

0 to −60

787

2000

2.4

−10 to −50

348

2000

2.4

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