Data Sheet

ADL5513

APPLICATIONS INFORMATION

analog.com

Rev. B | 17 of 25

Figure 34. Error vs. Temperature with Respect to Output Voltage at 25°C,

3600 MHz

With this alternative technique, the error at ambient becomes 0 dB

by definition. This would be valid if the device transfer function per-

fectly followed the ideal equation or if there were many calibration

points used.

VOUT = Slope × (PIN − Intercept)

(8)

Because the log amp never perfectly follows this equation, espe-

cially outside of its linear range, Figure 34 can be misleading as

a representation of log amp error. This plot tends to artificially

improve linearity and extend the dynamic range, unless enough

calibration points are used to remove error.

Figure 34 is a useful tool for estimating temperature drift at a

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

at ambient.

TEMPERATURE COMPENSATION OF OUTPUT

VOLTAGE

The primary component of the variation in VOUT vs. temperature

as the input signal amplitude is held constant is the drift of the

intercept. This drift is also a weak function of the input signal

frequency; therefore, a provision is made for the optimization of

the internal temperature compensation at a given frequency by

providing Pin TADJ with dual functionality. The first function for

this pin is temperature compensation and the second function is

to power down the device when VTADJ = VPOS − 0.3 V (see the

Power-Down Functionality section).

Figure 35. TADJ Interface

VTADJ is a voltage forced between TADJ and ground. The value

of this voltage determines the magnitude of an analog correction

coefficient, which is used to reduce intercept drift.

The relationship between output temperature drift and frequency is

not linear and cannot be easily modeled. As a result, experimenta-

tion is required to select the optimum VTADJ voltage.

The VTADJ voltage applied to Pin TADJ can be supplied by a DAC

with sufficient resolution, or Resistor R8 and Resistor R9 on the

evaluation board (see Figure 47) can be configured as a voltage

divider using VPOS as the voltage source.

Table 4 shows the recommended voltage values for some common-

ly used frequencies in characterization to optimize operation at

85°C. The TADJ pin has high input impedance.

Table 4. Recommended VTADJ Values

Frequency

Recommended VTADJ (V)

100 MHz

0.89

900 MHz

0.86

1.9 GHz

0.80

2.14 GHz

0.84

2.6 GHz

0.83

3.6 GHz

0.90

Compensating the device for temperature drift using TADJ allows

for great flexibility. If the user requires minimum temperature drift

at a given input power or subset of the dynamic range, the TADJ

voltage can be swept while monitoring VOUT over temperature.

Figure 36 shows how error changes on a typical part over the full

dynamic range when VTADJ is swept from 0.5 V to 1.2 V in steps of

0.1 V.