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AD8319 Scheda tecnica(PDF) 1 Page - Analog Devices |
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AD8319 Scheda tecnica(HTML) 1 Page - Analog Devices |
1 / 4 page Circuit Note CN-0082 Circuit Designs Using Analog Devices Products Apply these product pairings quickly and with confidence. For more information and/or support call 1-800-AnalogD (1-800-262-5643) or visit www.analog.com/circuit. Devices Connected/Referenced ADL5331 RF Variable Gain Amplifier (VGA) AD8319 45-dB RF Log Detector/Controller AD5621 12-Bit nanoDAC® Creating a Constant Envelope Signal Using the ADL5331 RFVGA and AD8319 Log Detector Rev. 0 “Circuits from the Lab” from Analog Devices have been designed and built by Analog Devices engineers. Standard engineering practices have been employed in the design and construction of eachcircuit,andtheirfunctionandperformance havebeentestedandverifiedinalabenvironment atroomtemperature.However,youaresolelyresponsible fortestingthe circuit anddetermining its suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due to anycausewhatsoeverconnectedtotheuseofany“CircuitfromtheLab”. (Continuedonlastpage) One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2009 Analog Devices, Inc. All rights reserved. CIRCUIT FUNCTION AND BENEFITS Overall performance of a transmitter, wired or wireless, is a strong function of the output power of the amplifier. If the signal is weak, bit error rate (BER) or modulation error rate (MER) will degrade due to low SNR. If the signal is too strong, distortion will cause the same issues. This circuit uses the ADL5331 VGA, the AD8319 power detector, and the AD5621 low power nanoDAC to generate output power control accurate to 12 bits. The AD8319 has very high temperature stability to compensate for any gain variation over temperature of the VGA, resulting in very accurate power control over a wide temperature range. Because the AD8319 control input VSET and the output VOUT are related to the RF input on a volts/dB scale and the AD5621 nanoDAC has a linear transfer function, the resulting output power control will be a linear-in-dB vs. DAC input code. CIRCUIT DESCRIPTION The ADL5331 variable gain amplifier provides accurate gain control. However, more precise regulation of output power is achieved with an automatic gain control (AGC) loop. Figure 1 shows the ADL5331 operating in an AGC loop. The addition of the AD8319 log amp allows the AGC to have improved temperature stability over a wide output power control range. To operate the ADL5331 VGA in an AGC loop, a sample of the output RF is back to the detector (typically using a directional coupler and additional attenuation). A setpoint voltage is applied by the AD5621 DAC to the VSET input of the detector while VOUT is connected to the GAIN pin of the ADL5331. Based on the detector’s defined linear-in-dB relationship between VOUT and the RF input signal, the detector adjusts the voltage on the GAIN pin (the detector’s VOUT pin is an error INLO INHI GAIN OPLO OPHI 23dB DIRECTIONAL COUPLER VPOS COMM ADL5331 +5V +5V +5V +5V COMM VOUT VPOS VSET INHI INLO CLPF AD8319 LOG AMP VOUT SYNC SCLK SDIN GND AD5621 12-BIT DAC VDD RF OUTPUT SIGNAL RF INPUT SIGNAL 1k Ω 490 Ω SETPOINT VOLTAGE 220pF 1nF 1nF 120nH 120nH 100pF 100pF 100pF 100pF ETC1-1-13 (M/A-COM) ETC1-1-13 (M/A-COM) Figure 1. ADL5331 Operating in an Automatic Gain Control Loop in Combination with the AD8319 and AD5621 (Simplified Schematic) |
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