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

Front-Panel Interface and is enabled (pulled low) whenever front-panel key selections indicate

that more than one harmonic board is being swept.

Voltage Reference U7 and associated circuitry provide a stable -7 V dc reference voltage for
both the Sweep Time and Aux Out Offset 

The control signal HSWP (High = Sweeping) is normally pulled low indicating the end of a
sweep by the 

 Trigger in the IF-Display Section. This signal can also be pulled low by

the Scan Test Circuit for the purpose of testing the scan circuitry.

If the scan ramp should exceed 

 V, this overvoltage is detected by 

 which triggers

one-shot multivibrator U6. U6 generates a 50 ms pulse on the HSWP line. When this pulse
goes low, the Al5 Controller “thinks” that the sweep has ended and performs its update

functions. When the pulse goes high again (after 50 ms), the Al5 Controller “thinks” a new

sweep has begun. This enables the sweep circuitry to function without the IF-Display Section,
or when a circuit malfunction exists, thus aiding troubleshooting.

The Scan Reset Amplifier supplies negative feedback that holds SCAN OUT (Q12 emitter) at

ground potential during retrace.

For Scan Generator (HP part number 85660-60198): Fixed-gain amplifier U13 amplifies
any potential at its noninverting input, pin 3. During retrace, LSAMPLE is low, and
sample-and-hold device U14 tracks the U13 output, charging 

This error voltage at 

 is divided by R64, R65, and R66, and is summed with the Span

Width DAC output at U12 pin 2. The amplified and inverted output of U12 cancels the
potential at SCAN OUT that produced the error voltage across 

When the sweep commences, 

 and LSAMPLE are high. The input to U14 is held on

 for the duration of the sweep.

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