ADL5903

Data Sheet

Rev. B | Page 18 of 20

After the slope and intercept are calculated (and stored in some

form) an equation can be used to calculate an unknown input

level based on the output voltage of the detector.

(4)

The log conformance error is the difference between this

straight line and the actual performance of the detector.

(5)

Figure 45 shows the log conformance error at five temperatures,

ranging from −55°C to +125°C, when using a two-point

calibration (calibration points are +10 dBm and −10 dBm)

measured at one temperature, 25°C. The error at the two

calibration points passes through 0 dB for the 25°C curve by

definition.

Multipoint calibration can be used to further extend the

measurement dynamic range. In this case, the transfer function

is segmented, with each segment having its own slope and

intercept. Figure 46 shows the error plot of the same device with

calibration points at −16 dBm, −4 dBm, and+12 dBm. The

three-point, dual-slope calibration results in tighter error

bounds over the high end of the range and extends the lower

measurement range to better than −20 dBm for ±1 dB error.

+85°C, and +125°C

For the example shown in Figure 46, the error drift with tempera-

ture is very small over the upper 20 dB of the measurement

range, varying ±0.3 dB, but widens at lower power levels, from

−20 dBm to −5 dBm to as high as ±0.9 dB. This is typical

performance, although some devices may perform better.

+25°C, −40°C, −55°C, +85°C, and +125°C

For comparison, the three-point calibration of a different device

is shown in Figure 47 for the same frequency and calibration

points. For this example, note that the device has greater

dynamic range, and the temperature dependence of error at

lower power levels is inverted.

Finally, Figure 48 shows the log conformance error at 2.14 GHz

for a collection of four devices at +25°C, −40°C, and +85°C with

three-point calibration (−16 dBm, −4 dBm, and+12 dBm). The

error plots at each temperature are calculated with respect to

the slope and intercept measurements from the 25°C line for

each device. This is consistent with a typical production

environment where calibration at one temperature is required.

Figure 48 illustrates the various error scenarios possible at low

input levels. The dynamic range of the three-point calibrated

devices extends to below −20 dBm for ±1.0 dB error.

Multiple Devices

20

15

10

5

0

–5

–10

–15

–20

–25

–30

–35

–40

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

6

5

4

3

2

1

0

–1

–2

–3

–4

–5

–6

–55°C

–40°C

+25°C

+85°C

+125°C

CALIBRATION AT –16dBm, –4dBm, AND +12dBm

20

15

10

5

0

–5

–10

–15

–20

–25

–30

–35

–40

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

6

5

4

3

2

1

0

–1

–2

–3

–4

–5

–6

–55°C

–40°C

+25°C

+85°C

+125°C

CALIBRATION AT –16dBm, –4dBm, AND +12dBm

20

15

10

5

0

–5

–10

–15

–20

–25

–30

–35

–40

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

6

5

4

3

2

1

0

–1

–2

–3

–4

–5

–6

–40°C

+25°C

+85°C

CALIBRATION AT –16dBm, –4dBm, AND +12dBm