APPLICATION NOTE APN2014: 6 Bit 63 dB RF Digital Attenuator Solution 500–2000 MHz High dynamic range systems often require an attenuator with a very wide attenuation range. It is possible to achieve 63 dB attenuation range by cascading two low cost digital attenuators, AA101-80 and AA104-73. It is effectively impossible to achieve such high attenuation range with a single package device. AA101-80 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 500 MHz to 2 GHz. VS V1 V5 V6 V7 R1 AA101-80 The AA104-73 offers unique design flexibility in a miniature SOT-6 package. This part may be tuned for different center frequencies by changing capacitors C2 and C3 (Table 1). Once the proper capacitance value is chosen for the desired frequency, the attenuation will cover a 150–200 MHz bandwidth. Performance for various values of capacitance is shown in the AA104-73 data sheet. The AA101-80 is a broadband device. Its attenuation will be flat over the frequency range from 500 MHz to 2.5 GHz. The cascade of AA104-73 and AA101-80 will exhibit a tuned response. See data plots (Figure 3). The example shown is for an operation at 900 MHz. This solution works with supply and control voltages of 3 to 5 V. The AA101-80 requires five lines of control and the AA104-73 requires two lines of complementary positive voltage, for a total of seven control lines. The truth table is shown in Table 2. AA104-73 C1 C3 C2 R1: 10 kΩ C1, C3: 47 pF C2: 12 pF RF Frequency (MHz) Bypass Capacitor Value C2 (pF) 900 12 1700 3.3 1800 2.7 1900 2.5 Table 1. Typical Capacitance for Desired RF Frequency Figure 1. Block Diagram, 6 Bit Attenuator, 900 MHz Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 200623 Rev. B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 1, 2007 1 APPLICATION NOTE • APN2014 Resistor, 10 kΩ R1 Connector, SMA East Coast Microwave 142-0701-851 2 Places C3 EVAL BOARD AA101-80 AA104-73 SK38760 REV 1 Test Board P/N SK38760 V5 V4 V3 1 C2 R1 V2 V1 MASK SET SK38762 REV 1 1 J2 V6 V7 VS AA104-73 C1 J1 Cut Trace Approx. 0.010 Wide, And Install Capacitor 3 Places C1, C2, C3 AA101-80 Solder 22 AWG. To Circuit Board 8 Places Figure 2. Assembly Test Board Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 2 August 1, 2007 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • 200623 Rev. B APPLICATION NOTE • APN2014 Typical Performance Data (0, 5 V) 900 MHz 0 2.00 -0.5 16 dB 63 dB VSWR (dB) Insertion Loss (dB) 1.80 -1.0 -1.5 -2.0 -2.5 J1–J2 1.60 32 dB 2 dB 1.40 1.20 0.88 0.92 0.96 1.00 0.80 1.00 0.92 0.96 Insertion Loss vs. Frequency VSWR vs. Frequency 70 0.75 60 63 dB 0.50 0.25 8 dB 0 2 dB 16 dB 4 dB 1 dB -0.50 32 dB -0.75 -1.00 0.80 0.88 Frequency (GHz) 1.00 -0.25 0.84 Frequency (GHz) Deviation from Nominal Insertion Phase (Deg.) Deviation from Nominal Attenuation (dB) 0.84 4 dB 1 dB Ins. Loss -3.0 -3.5 0.80 8 dB 50 1.00 63 dB 40 32 dB 30 20 8 dB 10 16 dB 4 dB 0 2 dB 1 dB -10 -20 0.84 0.88 0.92 0.96 -30 0.80 1.00 0.84 0.88 0.92 0.96 Frequency (GHz) Frequency (GHz) Attenuation Accuracy Attenuation Phase Accuracy 1.00 Figure 3 16 dB 8 dB 4 dB 2 dB 1 dB 32 dB V1 V2 V3 V4 V5 V6 V7 VHigh VHigh VHigh VHigh VHigh VHigh 0 Insertion Loss VHigh VHigh VHigh VHigh 0 VHigh 0 1 dB VHigh VHigh VHigh 0 VHigh VHigh 0 2 dB VHigh VHigh 0 VHigh VHigh VHigh 0 4 dB VHigh 0 VHigh VHigh VHigh VHigh 0 8 dB Attenuation State 0 VHigh VHigh VHigh VHigh VHigh 0 16 dB VHigh VHigh VHigh VHigh VHigh 0 VHigh 32 dB 0 0 0 0 0 0 VHigh 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 200623 Rev. 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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 4 August 1, 2007 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • 200623 Rev. B