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.
R1: 10 kΩ
C1, C3: 47 pF
C2: 12 pF
Figure 1. Block Diagram, 6 Bit Attenuator, 900 MHz
The AA104-73 offers unique design flexibility in a miniature
SOT-6 package. This part may be tuned for different center fre-
quencies 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
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 con-
trol 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.
RF Frequency (MHz)
Bypass Capacitor Value
Table 1. Typical Capacitance for Desired RF Frequency
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