Datasheet AD8364 (Analog Devices) - 31

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Data Sheet AD8364 TEMPERATURE COMPENSATION ADJUSTMENT VPSR
The AD8364 has a highly stable measurement output with
INTERNAL CURRENT
respect to temperature. However, when the RF inputs exceed a frequency of 600 MHz, the output temperature drift must be compensated for using ADJ[A, B] for optimal performance.
ADJ[A, B] VREF/2
Proprietary techniques are used to compensate for the temper- ature drift. The absolute value of compensation varies with
COMR
frequency, balun choice, and circuit board material. Table 5
IADJ[A, B]
05334-036 shows recommended voltages for ADJ[A, B] to maintain a Figure 68. ADJ[A, B] Interface Simplified Schematic temperature drift error of typically ±0.5 dB or better over the
DEVICE CALIBRATION AND ERROR CALCULATION
entire rated temperature range with the recommended baluns. The measured transfer function of the AD8364 at 2.14 GHz is
Table 5. Recommended Voltages for ADJ[A, B]
shown in Figure 69. The figure shows plots of both output
Frequency (MHz)
450 880 1880 2140 2500 voltage vs. input power and calculated error vs. input power. As
ADJ[A, B] (V)
0 0.5 0.65 0.85 1.10 the input power varies from −50 dBm to 0 dBm, the output voltage varies from 0.4 V to about 2.8 V. Compensating the device for temperature drift using ADJ[A, B] allows for great flexibility. If the user requires minimum temper- ature drift at a given input power or subset of the dynamic range,
3.50 2.0 BLUE = –40°C
the ADJ[A, B] voltage can be swept while monitoring OUT[A, B]
3.15 GREEN = +25°C 1.6 RED = +85°C ERROR CW –40°C
over temperature. Figure 67 shows the result of such an exercise
2.80 1.2
with a broadband balun, one that is not the recommended balun
2.45 0.8
at 1880 MHz. The value of ADJ[A, B] where the output has
) ERROR CW +25°C (V 2.10 0.4
minimum movement (approximately 0.77 V for the example in
ERROR CW +85°C OUTV 1.75
Figure 67) is the recommended voltage for ADJ[A, B] to achieve
0 VOUT2
minimum temperature drift at a given power and frequency.
1.40 –0.4 RROR (dB) E 1.70 1.05 –0.8 0.70 –1.2 +85°C VOUT1 1.65 0.35 –1.6 +65°C 0 –2.0 1.60 –60 –55 –50 –45 –40 –35 –30 –25 –20 –15 –10 –5 0 5 10 PIN MEAS (dBm)
04862-037
) +45°C INTERCEPT P P V IN1 IN2 1.55 +25°C
Figure 69. Transfer Function at 2.14 GHz.
OUTA ( 1.50 +10°C
Because slope and intercept vary from device to device, board- level calibration must be performed to achieve high accuracy.
–20°C 1.45
The equation for output voltage can be written as VOUT = Slope × (PIN − Intercept)
–40°C 1.40 0 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50
Where Slope is the change in output voltage divided by the
ADJA (V)
05334-035 change in power (dB), and Intercept is the calculated power at Figure 67. OUTA vs. ADJA over Temp. Pin = −30 dBm, 1.9 GHz which the output voltage is 0 V. (Note that Intercept is a theoretical The ADJ[A, B] input has high input impedance. The input can value; the output voltage can never achieve 0 V). be conveniently driven from an attenuated value of VREF using In general, the calibration is performed by applying two known a resistor divider, if desired. signal levels to the AD8364 input and measuring the corresponding Figure 68 shows a simplified schematic representation of the output voltages. The calibration points are generally chosen to ADJ[A, B] interface. be within the linear-in-dB operating range of the device (see the Specifications section for more details). Calculation of the slope and intercept is done using the equations: Slope = (VOUT1 − VOUT2)/(PIN1 − PIN2) Intercept = PIN1 − (VOUT1/Slope) Rev. C | Page 31 of 44 Document Outline FEATURES APPLICATIONS FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION SQUARE LAW DETECTOR AND AMPLITUDE TARGET RF INPUT INTERFACE OFFSET COMPENSATION TEMPERATURE SENSOR INTERFACE VREF INTERFACE POWER-DOWN INTERFACE VST[A, B] INTERFACE OUT[A, B, P, N] OUTPUTS MEASUREMENT CHANNEL DIFFERENCE OUTPUT USING OUT[P, N] CONTROLLER MODE RF MEASUREMENT MODE BASIC CONNECTIONS CONTROLLER MODE BASIC CONNECTIONS Automatic Power Control Automatic Gain Control CONSTANT OUTPUT POWER OPERATION GAIN-STABLE TRANSMITTER/RECEIVER TEMPERATURE COMPENSATION ADJUSTMENT DEVICE CALIBRATION AND ERROR CALCULATION SELECTING CALIBRATION POINTS TO IMPROVE ACCURACY OVER A REDUCED RANGE CHANNEL ISOLATION ALTERING THE SLOPE CHOOSING THE RIGHT VALUE FOR CHP[A, B] AND CLP[A, B] RF BURST RESPONSE TIME SINGLE-ENDED INPUT OPERATION PRINTED CIRCUIT BOARD CONSIDERATIONS PACKAGE CONSIDERATIONS DESCRIPTION OF CHARACTERIZATION BASIS FOR ERROR CALCULATIONS EVALUATION BOARD OUTLINE DIMENSIONS ORDERING GUIDE