Agilent Technologies VXI E1439 - Manual (Page 222)

212
Module Description
Block diagram and description
Input
When baseband mode is selected, the input signal goes through the lower path on the diagram
below. In this mode, there is only one input range and the anti-alias filter (36 MHz bandwidth) can
be switched out.
The baseband input is terminated by the input amplifier that follows the baseband anti-alias filter.
The bandwidth of the baseband input is 36 MHz. There is no variable attenuation for the baseband
path. This results in a single range for baseband mode.
When 70 MHz IF mode is selected, the input signal goes through the upper path on the diagram
below. Amplifiers and attenuators allow the full-scale range to be set with 1 dB resolution. The
70 MHz IF input is terminated by either a preamp or a programmable attenuator, either of which
follows a 52 MHZ high pass filter.
The combination of the pre-amplification and programmable attenuation results in the 0 to 48
ranges setting for the 70 MHz IF mode. After this, a combination of low pass and high pass filters
realizes the 70 MHz IF filter (in a 52 to 88 MHz pass band that provides anti-alias protection).
Signals within the pass band are next downconverted by a mixer with a fixed 95 MHz LO
frequency. The mixer translates the 52 to 88 MHz span to 43 to 7 MHz. The mixer output is low
pass filtered, preserving the 43 to 7 MHz band, and amplified before being sampled by the A to D
converter at a 95 MHz sample rate.