Datasheet LTC5582 (Analog Devices) - 11

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APPLICATIONS INFORMATION
The LTC5582 is a true RMS RF power detector, capable
Table 1. Single-Ended Input Impedance (DEC Floating)
of measuring an RF signal over the frequency range from
FREQUENCY INPUT IMPEDANCE S11
40MHz to 10GHz, independent of input waveforms with
(MHZ) (Ω) MAG ANGLE (˚)
different crest factors such as CW, CDMA2K, WCDMA, 40 220.7-j63.0 0.655 –7.0 LTE and WiMAX signals. Up to 60dB dynamic range is 100 195.2-j47.3 0.611 –7.1 achieved with a very stable output within the full tempera- 200 175.1-j37.6 0.571 –7.3 ture range from –40°C to 125°C. Its sensitivity can be as 400 200.9-j42.2 0.618 –6.3 low as –57dBm up to 2.7GHz even with single-ended 50Ω 600 159.8-j52.9 0.563 –11.5 input termination. 800 154.8-j52.4 0.554 –12.2 1000 158.6-j57.1 0.568 –12.4
RF Inputs
1200 164.1-j81.1 0.612 –14.7 The differential RF inputs are internally biased at 1.585V. 1400 138.1-j110.5 0.650 –21.0 The differential impedance is 400Ω. These pins should be 1600 102.7-j113.3 0.659 –28.5 DC blocked when connected to ground or other matching 1800 80.1-j103.1 0.647 –35.3 components. 2000 67.1-j92.0 0.628 –41.3 The LTC5582 can be driven in a single-ended configuration 2200 58.4-j82.3 0.607 –46.7 as illustrated in Figure 3. The single-ended input impedance 2400 52.9-j74.5 0.586 –52.0 vs frequency is detailed in Table 1. The DEC Pin can be 2600 48.5-j67.6 0.566 –57.0 either left floating or AC-coupled to ground via an external 2800 44.8-j61.5 0.546 –62.0 capacitor. While the RF signal is applied to the IN+ (or IN–) 3000 41.8-j56.1 0.526 –66.9 Pin, the other pin IN– (or IN+) should be AC-coupled to 3200 41.8-j56.3 0.508 –72.0 ground. By simply terminating a 68Ω resistor between 3400 37.3-j47.0 0.490 –77.1 the IN+ and IN– Pins and coupling the non-signal side 3600 35.4-j42.9 0.473 –80.2 to ground using a 1nF capacitor, broadband 50Ω input 3800 33.9-j39.1 0.457 –87.7 matching can be achieved with typical return loss better 4000 32.4-j35.5 0.445 –93.1 than 10dB from 40MHz to 5.5GHz. At higher RF frequen- 4200 31.1-j32.3 0.429 –98.8 cies, additional matching components may be needed. 4400 29.9-j29.1 0.416 –104.7 4600 28.9-j26.2 0.405 –110.7 LTC5582 VCC 4800 27.9-j23.3 0.395 –117.0 J1 C4 RF INPUT 1nF 5000 27.0-j20.5 0.388 –123.5 IN+ 2 5200 26.2-j17.8 0.382 –130.2 C5 200Ω 5400 25.4-j15.2 0.376 –136.9 DEC R4 3 5600 24.7-j12.6 0.376 –144.1 68Ω 50pF 5800 24.0-j10.0 0.377 –151.3 200Ω IN– 4 6000 23.3-j7.5 0.377 –158.4 C9 C8 OPTIONAL 1nF The LTC5582 differential inputs can also be driven from 5582 F03 a fully balanced source as shown in Figure 4. When the
Figure 3. Single-Ended Input Configuration
signal source is a single-ended 50Ω, conversion to a dif- ferential signal can be achieved using a 1:8 balun to match the internal 400Ω input impedance to the 50Ω source. This impedance transformation results in 9dB voltage gain, thus 9dB improvement in sensitivity is obtained Rev. B For more information www.analog.com 11 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Electrical Characteristics Pin Configuration Typical Performance Characteristics Pin Functions Test Circuits Applications Information Package Description Revision History Typical Application Related Parts