APPLICATION NOTE APN2013: 6 Bit 63 dB IF Digital Attenuator Solution 1–500 MHz High dynamic range systems often require an attenuator with a very large attenuation range. It is possible to achieve 63 dB attenuation range by cascading two low cost Skyworks digital attenuators, AA260-85 and AA104-73. It is effectively impossible to achieve such high attenuation range with a single package device. AA260-85 is a 5-bit attenuator with a 1 dB least significant bit (LSB). Full scale attenuation for this attenuator is 31 dB. AA104-73 is a 1-bit digital attenuator that produces 32 dB attenuation. When these two attenuators are cascaded on a standard FR4 printed circuit board, 63 dB total attenuation range with 1 dB step size is produced within the frequency range 1 MHz to 500 MHz. The AA104-73 offers unique design flexibility in a miniature SOT-6 package. This part may be tuned for different IF frequencies by changing capacitors C2 and C3 (Table 1). Once the proper capacitance value is chosen for the desired frequency, the operating bandwidth of this attenuator is 150–200 MHz. Performance for various values of capacitance is shown in the AA104-73 data sheet. VS V1 V9 V10 V11 The AA260-85 is a broadband device. Its attenuation is flat over the frequency range from 300 kHz to 2 GHz. The cascade of AA104-73 and AA260-85 exhibits a tuned response. See data plots (Figure 3). The example shown is for operation at 242 MHz. This solution works with supply and control voltages of 3 to 5 V. The AA260-85 requires nine lines of complementary control voltages (two control lines per bit, only one control line for the LSB) and the AA104-73 requires two lines of complementary positive voltage, for a total of 11 control lines. The truth table is shown in Table 2. AA260-85 operates with negative control voltage. The attenuator may be operated with positive control voltage by “floating” the device with DC block capacitors in the signal path (C1 and C4) and in the ground connections (C2). IF Frequency (MHz) Bypass Capacitor Value C2, C3 (pF) 450 250, 82 242 680, 220 131 3000, 1000 70 4700, 1500 R1 Table 1. Typical Bypass Capacitor for a Given IF AD260-85 AA104-73 C1 C4 C2 C3 R1: 10 kΩ C1, C2, C4: 680 pF C3: 220 pF Figure 1. Block Diagram, 6 Bit Attenuator, 242 MHz Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 200622 Rev. B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 27, 2007 1 APPLICATION NOTE • APN2013 Resistor, 10 kΩ R1 V10 V11 AA104-73 Connector, SMA East Coast Microwave 142-0701-851 2 Places C4 C3 Test Board P/N SK38761 V1 V2 V3 V4 V5 V6 V7 V8 V9 EVAL BOARD AD260-85 AA104-73 1 SK38761 REV 1 C1 MASK SET SK38762 R1 REV 1 1 C2 J2 J1 VS Cut Trace Approx. 0.010 Wide, And Install Capacitor 4 Places C1, C2, C3, C4 AD260-85 Solder 22 AWG To Circuit Board 12 Places Figure 2. Assembly Test Board Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 2 July 27, 2007 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • 200622 Rev. B APPLICATION NOTE • APN2013 Typical Performance Data (0, 5 V) 242 MHz 2.00 0 -0.5 VSWR (dB) Insertion Loss (dB) 1.80 -1.0 -1.5 J1–J2 -2.0 1.60 32 dB 8 dB 1.40 63 dB 4 dB 2 dB -2.5 1.20 Ins. Loss -3.0 1 dB 1.00 -3.5 0.18 0.20 0.22 0.24 0.26 0.28 0.30 0.18 0.22 0.24 0.26 0.28 Frequency (GHz) Insertion Loss vs. Frequency VSWR vs. Frequency 1.00 30 0.75 20 0.50 0.25 2 dB 0 0.20 Frequency (GHz) Deviation from Nominal Insertion Phase (Deg.) Deviation from Nominal Attenuation (dB) 16 dB 4 dB 8 dB 16 dB 1 dB 32 dB -0.25 -0.50 63 dB -0.75 0.30 32 dB 10 1 dB 0 4 dB 2 dB 16 dB -10 8 dB -20 -30 63 dB -40 -50 -60 -1.00 0.18 0.20 0.22 0.24 0.26 0.28 -70 0.18 0.30 0.20 0.22 0.24 0.26 0.28 Frequency (GHz) Frequency (GHz) Attenuation Accuracy Attenuation Phase Accuracy 0.30 Figure 3 1 dB 2 dB 4 dB 8 dB 16 dB 32 dB V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 Atten. State 0 0 VHigh 0 VHigh 0 VHigh 0 VHigh 0 VHigh Ins. Loss VHigh 0 VHigh 0 VHigh 0 VHigh 0 VHigh 0 VHigh 1 dB 0 VHigh 0 0 VHigh 0 VHigh 0 VHigh 0 VHigh 2 dB 0 0 VHigh 5 0 0 VHigh 0 VHigh 0 VHigh 4 dB 0 0 VHigh 0 VHigh VHigh 0 0 VHigh 0 VHigh 8 dB 0 0 VHigh 0 VHigh 0 VHigh VHigh 0 0 VHigh 16 dB 0 0 VHigh 0 VHigh 0 VHigh 0 VHigh VHigh 0 32 dB VHigh VHigh 0 VHigh 0 VHigh 0 VHigh 0 VHigh 0 63 dB VHigh = +3 to +5 V (VS = VHigh ± 0.2 V). Table 2. Truth Table Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 200622 Rev. B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • July 27, 2007 3 APPLICATION NOTE • APN2013 Copyright © 2002, 2003, 2004, 2005, 2006, 2007, Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. 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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 4 July 27, 2007 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • 200622 Rev. B