Filter
Top Products
Theory of Operation
3-34
2715 Spectrum Analyzer Service Manual
RF OPTIONS
1dBStep
0
2
4
6
8
10
5MHz
300 kHz
30 kHz
3kHz
10 MHz/−10 dBm
to Log Amp
PIN Diode
Attenuator
10 MHz/−20 dBm from RF Mother Board
1 MHz, 100 kHz, 10 kHz, 1 kHz,
and 300 Hz Filters
10
10
10
1010
Figure 3- 15: Variable Resolution Module Diagram
The PIN attenuator design is based upon a pair of matched pin diodes used in a
tee configuration. This configuration maintains the impedance match at each end,
providing the product of the PIN diode resistances is equal to the square of the
end terminations. This can be approximated if the sum of the currents in the PIN
diodes is equal to a constant. The DAC has complementary current outputs
whose total is set by an adjustment. The attenuation range is approximately
12 dB with a 1 dB minimum loss. The worst case return loss at the end points is
15 dB. The step size for an 8 bit DAC is 0.04 dB steps in the center of its range.
PIN Attenuator