HP (Hewlett-Packard) HP 85660B ユーザーズマニュアル

The RF attenuator driver is similar to the RF Switch driver. The major difference is the logic
decoding to the inputs of the darlington switch drivers. The input to the logic circuit is the
standard 10, 20, 40, 

 attenuation logic levels. The logic circuit 

 

decodes this to the 

10,

20, 20, 20, 

 attenuation logic levels required to drive the RF attenuator. The output drivers

consist of darlington amplifiers driven by the outputs of 

 or the inverted outputs of 

 via

U3. A low output of a darlington turns that line on. That is, a low at 

 pin 13, coupled

with high at 

 pin 11, enables the 10 

 attenuation position, and so forth.

The power down circuit switches the RF attenuator into a 40 

 attenuation position to

prevent accidental damage to 

 YTX or 

 First Converter from an input signal when

the instrument is off. When the power up signal goes low, U3 pin 10 is driven high which
turns on 

 and Q13, forcing 

 pins 

 and 9, U4 pin 7, and U3 pin 5 high. This forces at

least the last two 20 

 attenuation stages in the attenuator on.

On power up, the instrument goes through a self-check program. To prevent the RF relays

and the attenuator from chattering during this time, the 

 V Bias to the attenuator and

RF switch is delayed for about 2.5 seconds after the power up signal goes high. This delay is
caused by R59 and 

 When power up goes high, it takes approximately 2.5 seconds for the

voltage across 

 to charge up enough to turn on 

 

 output is inverted twice by the

darlington amplifiers 

 and 

 so that when 

 output drops, 

 output also drops

turning on 

 which applies the 

 V to the relay circuits.