ADL5519ACPZ-R7 datasheet(25/39 Pages) AD

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Data Sheet

ADL5519

Rev. C | Page 25 of 39

Another way of presenting the error function of a log amp detector

is shown in Figure 62. In this example, the decibel (dB) error at

hot and cold temperatures is calculated with respect to the output

voltage at ambient. This is a key difference when compared to

the previous plots, in which all errors have been calculated with

respect to the ideal transfer function at ambient.

2.00

1.75

1.50

1.25

1.00

0.75

0.50

0.25

2.0

1.5

1.0

0.5

–0.5

–1.0

–1.5

–2.0

–60

–50

–40

–30

–20

–10

PIN (dBm)

Figure 62. Error vs. Temperature with Respect to Output Voltage at 25°C,

2.14 GHz (Removes Transfer Function Nonlinearities at 25°C)

With this alternative technique, the error at ambient becomes,

by definition, equal to 0 (see Figure 62). This value would be

valid if the device transfer function perfectly followed the ideal

of the VOUT = Slope × (PIN − Intercept) equation.

However, because an rms amp, in practice, never perfectly follows

this equation (especially outside of its linear operating range), this

plot tends to artificially improve linearity and extend the

dynamic range, unless enough calibration points are taken to

remove the error.

Figure 62 is a useful tool for estimating temperature drift at

a particular power level with respect to the (nonideal) output

voltage at ambient.

TEMPERATURE COMPENSATION ADJUSTMENT

The ADL5519 temperature performance has been optimized to

ensure that the output voltage has minimum temperature drift

at −10 dBm input power. The applied voltage for the ADJA and

ADJB pins for some specified frequencies is listed in Table 4.

However, not all frequencies are represented in Table 4, and

experimentation may be required.

Compensating the device for temperature drift by using ADJA,

ADJB allows for great flexibility. To determine the optimal adjust

voltage, sweep ADJA, ADJB at ambient and at the desired

temperature extremes for a couple of power levels while

monitoring the output voltage. The point of intersection

determines the best adjust voltage. Some additional minor

tweaking may be required to achieve the highest level of tempera-

ture stability. With appropriate values, a temperature drift error

of typically ±0.5 dB over the entire rated temperature range can be

achieved.

Table 4. Recommended ADJA, ADJB Voltage Levels

Frequency

Recommended ADJA, ADJB Voltage (V)

100 MHz

0.65, 0.7

900 MHz

0.6, 0.65

1.9 GHz

0.5, 0.55

2.2 GHz

0.48, 0.6

3.6 GHz

0.35, 0.42

5.8 GHz

0.58, 0.7

8 GHz

0.72, 0.82

Proprietary techniques are used to compensate for the temperature

drift. The absolute value of compensation varies with frequency

and circuit board material.

ADJA, ADJB are high impedance pins. The applied ADJA, ADJB

voltages can be supplied from VREF through a resistor divider.

Figure 63 shows a simplified schematic representation of the

ADJA, ADJB interface.

VREF

ICOMP

VTADJ

COMR

ADJA, ADJB

ADL5519

COMR

Figure 63. ADJA, ADJB Interface Simplified Schematic

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