A6All

A6All Slope Generator, Circuit Description

The slope generator takes a voltage which is proportional to YTX frequency and produces a current to control the slope attenuator in the A6A3 Last Converter, which compensates for conversion loss variations of the input mixer within each frequency band. The slope generator also has circuitry which decodes bandswitch and attenuator settings, produces pulses for

the sample and hold, and hysteresis circuits in the A6A12 YTX Driver, produces the YTX peaking signal for the YTX Driver, and a signal to switch in the filter capacitor on the A6A7 YTX Current Driver.

Bandswitch and Attenuator Decode @

U9 is a hex latch which receives six lines from the 50-wire Instrument Bus and a strobe, LCK2, which goes low when the six lines have valid A6 RF Module information. Three of the latch outputs have attenuator setting information and go to the A6AlO Miscellaneous Bias/Relay Driver. The other three lines have bandswitch information which is decoded by U3A and U3B.

U3B decodes the low band (Band A, 0 to 2.5 GHz) and the external mixer band (Band F). When pin 2 of U9 is high and pin 12 is low, Band A is selected. The output of U3B is high, turning Q22 on, bringing the collector of Q22 low. This turns Q19 off, bringing the collector of Q19 (LO BAND) high. This information goes to the A6AlO Miscellaneous Bias/Relay Driver to control the A6Al RF input switch. Q20 inverts the signal and drives amplifier A4A, producing a signal which is approximately +17 V when Band A is valid and approximately

-8 V otherwise. This signal is used throughout the A6All Slope Generator. When pins 2 and 12 of U9 are both high, Band F is active. The output of U3B is low, turning Q22 off, and bringing the collector of Q22 (and Band F line) high. At the same time,me, Q19 turns on, bringing the LO BAND line low.

U3A decoder is enabled when pin 2 of U9 is low. Pins 5 and 12 of U9 have coded information giving harmonic numbers as shown in Table 1.

Table 1. Bandswitch Decoding

Band B2 (pin 12) Bl (pin 5) N

B 01 1

C 10 2

D 11 3

E 00 4

A6A11 1