A6A12

A6A12 YIG-Tuned Mixer (YTX) Driver, Circuit Description

The YTX Driver receives a voltage proportional to the instrument LO frequency and produces a signal to control current in the YTX coil.

Input Differential Amplifier @

This input signal to the YTX Driver comes from the A19 DAC and is -3 V/GHz. For example, as the YTO Loop sweeps from 2 to 6 Ghz, this input signal sweeps from -6 to -18 V. It is buffered by differential amplifier UlA, and appears at TPl.

Bandswitch @

The frequency that the YTX is tuned to must be made to follow the first, second, third, or fourth harmonic of the YTO frequency, depending on the frequency band in which the instrument is operating. This is done by attenuating the buffered input signal with a voltage divider as shown in Figure 1.

R5

TPl2K

-3V/GHz(LO) 0

 

0

 

R7

1K

R8

 

1K

* -.525V/GHz(YTX)

0

R9

1K

0

RlO 1K

Figure 1. Bandwidth Voltage Divider

The position on the attenuator is determined by the harmonic number in use. The bandswitching is done with FET Ql, Q2, Q3, and Q12. The bandswitch information used to turn on the FETs comes from A6All Slope Generator. R6 and Rll to R14 form a second voltage divider used as a gate return through R15 to R18. This prevents current through bandswitch diodes and resistors (for example, R19 and CRl) when the associated FET is switched off from affecting the bandswitch voltage divider R5 and R7 to RlO.

A6A12 1