AD8363ACPZ-R7 datasheet(18/36 Pages) AD

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AD8363

Rev. 0 | Page 18 of 36

TEMPERATURE SENSOR INTERFACE

The AD8363 provides a temperature sensor output with an

output voltage scaling factor of approximately 5 mV/°C. The

output is capable of sourcing 4 mA and sinking 50 μA maximum at

temperatures at or above 25°C. If additional current sink capability

is desired, an external resistor can be connected between the

TEMP and COMM pins. The typical output voltage at 25°C is

approximately 1.4 V.

TEMP

VPOS

COMM

INTERNAL

VPAT

12k

Ω

Figure 45. TEMP Interface Simplified Schematic

VREF INTERFACE

The VREF pin provides an internally generated voltage reference.

The VREF voltage is a temperature stable 2.3 V reference that is

capable of sourcing 4 mA and sinking 50 μA maximum at

temperatures at or above 25°C. An external resistor can be

connected between the VREF and COMM pins to provide

additional current sink capability. The voltage on this pin can be

used to drive the TCM1, TCM2/PWDN, and VTGT pins, if desired.

INTERNAL

VOLTAGE

16k

Ω

VREF

VPOS

COMM

Figure 46. VREF Interface Simplified Schematic

TEMPERATURE COMPENSATION INTERFACE

While the AD8363 has a highly stable measurement output with

respect to temperature, it uses proprietary techniques to make it

even more stable. For optimal performance, the output temperature

drift must be compensated for using the TCM1 and TCM2/

PWDN pins. The absolute value of compensation varies with

frequency and VTGT. Table 4 shows the recommended voltages for

the TCM1 and TCM2/PWDN pins to maintain the best

temperature drift error over the rated temperature range (−40°C <

TA < 85°C) when driven single-ended and using a VTGT = 1.4 V.

Table 4. Recommended Voltages for TCM1 and TCM2/PWDN

Frequency

TCM1 (V)

TCM2/PWDN (V)

100 MHz

0.47

1.0

900 MHz

0.5

1.2

1.9 GHz

0.52

0.51

2.14 GHz

0.52

0.6

2.6 GHz

0.54

1.1

3.8 GHz

0.56

1.0

5.8 GHz

0.88

1.0

The values in Table 4 were chosen to give the best drift

performance at the high end of the usable dynamic range

over the −40°C to +85°C temperature range.

Compensating the device for the temperature drift using TCM1

and TCM2/PWDN allows for great flexibility and the user may

wish to modify these values to optimize for another amplitude

point in the dynamic range, for a different temperature range,

or for an operating frequency other than those shown in Table 4.

To find a new compensation point, VTCM1 and VTCM2 can be

swept while monitoring VOUT over the temperature at the

frequency and amplitude of interest. The optimal voltages for

VTCM1 and VTCM2 to achieve minimum temperature drift at a given

power and frequency are the values of VTCM1 and VTCM2 where

VOUT has minimum movement. See the AD8364 and ADL5513

data sheets for more information.

Varying VTCM1 and VTCM2 has only a very slight effect on VOUT at

device temperatures near 25°C; however, the compensation circuit

has more and more effect, and is more and more necessary for

best temperature drift performance, as the temperature departs

farther from 25°C.

Figure 47 shows the effect on temperature drift performance at

25°C and 85°C as VTCM1 is varied but VTCM2 is held constant at 0.6 V.

–1

–2

–3

–60

–50

–40

–30

–20

–10

RFIN (dBm)

25°C

85°C

VTCM1 = 0.62V

VTCM1 = 0.42V

Figure 47. Error vs. Input Amplitude over Stepped VTCM1 Values,

25oC and 85oC, 2.14 GHz, VTCM2 = 0.6 V

TCM1 primarily adjusts the intercept of the AD8363 at

temperature. In this way, TCM1 can be thought of as a coarse

adjustment to the compensation. Conversely, TCM2 performs a

fine adjustment. For this reason, it is advised that when searching

for compensation with VTCM1 and VTCM2, that VTCM1 be adjusted

first, and when best performance is found, VTCM2 can then be

adjusted for optimization.

It is evident from Figure 47 that the temperature compensation

circuit can be used to adjust for the lowest drift at any input

amplitude of choice. Though not shown in Figure 47, a similar

analysis can simultaneously be performed at −40°C, or any

other temperature within the operating range of the AD8363.

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