Data Sheet

ADL5513

APPLICATIONS INFORMATION

analog.com

Rev. B | 15 of 25

the pull-down resistance at VOUT. There is an internal pull-down

resistor of 1.6 kΩ. A resistive load at VOUT is placed in parallel

with the internal pull-down resistor to provide additional discharge

current.

Figure 28. Output Interface

The ADL5513 output can drive over 1 nF of capacitance. When

driving such high output capacitive loads, it is required to capaci-

tively load the CLPF pin. The capacitance on the CLPF pin should

be at least 1/50th that of the capacitance on the VOUT pin.

SETPOINT INTERFACE

The VSET input drives the high impedance (40 kΩ) input of an

internal op amp. The VSET voltage appears across the internal 3.5

kΩ resistor to generate ISET. When a portion of VOUT is applied to

VSET, the feedback loop forces

ID × log10(VIN/VINTERCEPT) = ISET

(3)

If VSET = VOUT/2x, ISET = VOUT/(2x × 3.5 kΩ).

The result is VOUT = (ID × 3.5 kΩ × 2x) × log10(VIN/VINTERCEPT).

Figure 29. VSET Interface

The slope is given by ID × 2x × 3.5 kΩ = 20 mV/dB × x. For

example, if a resistor divider to ground is used to generate a

VSET voltage of VOUT/2, then x = 2. The slope is set to 800 mV/

decade or 40 mV/dB. See the Measurement Mode section for more

information on setting the slope in measurement mode.

DESCRIPTION OF CHARACTERIZATION

The general hardware configuration used for most of the ADL5513

characterization is shown in Figure 30. The signal source and

power supply used in this example are the Agilent E8251A PSG

signal generator and E3631A triple output power supply. Output

voltage was measured using the Agilent 34980A switch box.

Figure 30. General Characterization Configuration

ERROR CALCULATIONS

The measured transfer function of the ADL5513 at 100 MHz is

shown in Figure 31. The figure shows plots of measured output

voltage, calculated error, and an ideal line. The input power and

output voltage are used to calculate the slope and intercept values.

The slope and intercept are calculated using linear regression over

the input range from −40 dBm to −20 dBm. The slope and intercept

terms are used to generate an ideal line. The error is the difference

in measured output voltage compared to the ideal output line.

Figure 31. Typical Output Voltage vs. Input Signal

The equation for output voltage can be written as

VOUT = Slope × (PIN − Intercept)

(4)

where:

Slope is the change in output voltage divided by the change in input

power, PIN. Slope is expressed in volts per decibel (V/dB).

Intercept is the calculated power in decibels (dB) at which the

output voltage is 0 V. Note that VOUT = 0 V can never be achieved.

Calibration is performed by applying two known signal levels to the

ADL5513 and measuring the corresponding voltage outputs. The

calibration points are in general chosen to be within the linear-in-dB

range of the device.

Calculation of the slope and intercept are accomplished by using

the following equations:

Slope=VOUTMEASURED1−VOUTMEASURED2

PIN1−PIN2

(5)