link to page 22 link to page 22 link to page 22 link to page 23 Data SheetAD8362 An external 100 Ω shunt resistor combines with the internal 3.003.02.8GHz 100 Ω single-ended input impedance to provide a broadband 2.752.53.45GHz3.65GHz 50 Ω match. The unused input (in this case, INLO) is ac-coupled 2.502.0 to ground. Figure 49 shows the transfer function of the AD8362 2.251.5 at various frequencies when the RF input is driven single- 2.001.0 ended. The results show that transfer function linearity at the 1.750.5dB)T (V)R ( top end of the range is degraded by the single-ended drive. U 1.500VO 1.25–0.54.02.0ERRO450MHz1.00–1.01900MHz3.52500MHz1.50.75–1.5900MHz2140MHz0.50–2.03.01.00.25–2.52.50.50–3.0dB)–60 –55 –50 –45 –40 –35 –30 –25 –20 –15 –10 –50510 15 051 T (V)R (U 2.00INPUT AMPLITUDE (dBm) 02923- VOERRO Figure 51. Transfer Function at Various Frequencies ≥2.7 GHz when 1.5–0.5 the RF Input is Driven Single-Ended 1.0–1.0OPERATION AT LOW FREQUENCIES0.5–1.5 In conventional rms-to-dc converters based on junction tech- 0–2.0 niques, the effective signal bandwidth is proportional to the –55 –50 –45 –40 –35 –30 –25 –20 –15 –10 –50510 049 signal amplitude. In contrast, the 3.5 GHz VGA bandwidth in PIN (dBm) 02923- the AD8362 is independent of its gain. Because this amplifier is Figure 49. Transfer Function at Various Frequencies when the internally dc-coupled, the system is also used as a high accuracy RF Input is Driven Single-Ended rms voltmeter at low frequencies, retaining its temperature- AD8362 stable, decibel-scaled output (for example, in seismic, audio, 1 COMMACOM 160.01µF and sonar instrumentation). 2 CHPFVREF 151nF3 DECLVTGT 14RF INPUT While the AD8362 can be operated at arbitrarily low frequencies, 2.7nH4 INHIVPOS 13 an ac-coupled input interface must be maintained. In such cases, 1nF1nF5 INLOVOUT 124.7nH the input coupling capacitors should be large enough so that the 1nF6 DECLVSET 11 lowest frequency components of the signal to be included in the 7 PWDNACOM 10 measurement are minimal y attenuated. For example, for a 3 dB 8 COMMCLPF 9 reduction at 1.5 kHz, capacitances of 1 µF are needed because the 050 input resistance is 100 Ω at each input pin (200 Ω differential y), 02923- Figure 50. Input Matching for Operation at Frequencies ≥2.7 GHz and the calculation is 1/(2π × 1.5 kΩ × 100) = 1 μF. In addition, to lower the high-pass corner frequency of the VGA, a large capaci- For operation at frequencies ≥2.7 GHz, some additional tor must be connected between the CHPF pin and ground (see components are required to match the AD8362 input to 50 Ω the Choosing a Value for CHPF section). (see Figure 50). As the operating frequency increases, there is also corresponding shifting in the operating power range (see More information on the operation of the AD8362 and other Figure 51). RF power detectors at low frequency is available in AN-691 Application Note, Operation of RF Detector Products at Low Frequency. Rev. F | Page 21 of 33 Document Outline FEATURES APPLICATIONS FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS EQUIVALENT CIRCUITS TYPICAL PERFORMANCE CHARACTERISTICS CHARACTERIZATION SETUP EQUIPMENT ANALYSIS CIRCUIT DESCRIPTION SQUARE LAW DETECTION VOLTAGE vs. POWER CALIBRATION OFFSET ELIMINATION TIME-DOMAIN RESPONSE OF THE CLOSED LOOP OPERATION IN RF MEASUREMENT MODE BASIC CONNECTIONS DEVICE DISABLE RECOMMENDED INPUT COUPLING Choosing Input Coupling Capacitors Single-Ended Input Drive OPERATION AT LOW FREQUENCIES CHOOSING A VALUE FOR CHPF CHOOSING A VALUE FOR CLPF ADJUSTING VTGT TO ACCOMMODATE SIGNALS WITH VERY HIGH CREST FACTORS ALTERING THE SLOPE TEMPERATURE COMPENSATION AND REDUCTION OF TRANSFER FUNCTION RIPPLE TEMPERATURE COMPENSATION AT VARIOUS WiMAX FREQUENCIES UP TO 3.8 GHz OPERATION IN CONTROLLER MODE RMS VOLTMETER WITH 90 dB DYNAMIC RANGE AD8362 EVALUATION BOARD OUTLINE DIMENSIONS ORDERING GUIDE