Tektronix 2715 RF Options

Theory of Operation

2715 Spectrum Analyzer Service Manual 3-35

The 10 dB gain step stages incorporat ea tran sformer feedback amplifier. These

stages have approximately 0.5 dB of loss or 9.5 dB of gain, for a net difference

of 10 dB. When the gain step is selected, thesignal is routed through the

amplifier for a gainof approximately 11.5 dB. A pad of approximately 1.5 dB is

added to trim the gain down to 10 dB. The signal is then routedthrough a switch

that has approximately 0.5 dB of loss. When the amplifieris deselected, the

signal is routed around the amplifier,thus preserving noise figure and intercept

point. A total of five step gain stages are used.

The 1 dB gain step amplifier is the last amplifier before the filterswitching tree.

The amplifier is composed of a class AB, three stage, feedback amplifi er.The

gain is adjusted in 2 dB steps for a total of10 dB . The 1 dB steps aredone by

shunting part of the signal to ground. This is controlledby Q246, located at the

input of this amplifier.This configuration allows the entire 10 dB gain sequence

to be contained within one step gain stage.

The routing switches are usedto route RF signals to various areas. They are

composed of a transistor in heavy saturat ion that has relatively large charge

storage characteristics.The topology used is a shunt series configuration. These

switches are used on both the input andoutput of each filter including the

external filter connection.

RF Options

The RF Options is a system of additional resolution bandwidth filtersthat

enhance the measurementcapability of the instrument. See Figure 3--16.