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

The sweep ramp is formed by alternately charging and discharging Cl, according to the
following cycle.

Control line HSWP resets the sweep (High = Sweeping). When HSWP goes low (determined

by IF-Display Section), LHOLD 

 pin 8)  oes low, turning on 

 When CR1 is on,

charging current bypasses ramping capacitor Cl and instead passes to ground via 
Ramping capacitor Cl stops charging.

Ramping capacitor Cl holds its charge until LANR, from Front-Panel Interface Assembly

A12, goes low (Low = Analog Reset). When LANR goes low, LHOLD goes high, turning

CR1 off, removing the current bypass for ramping capacitor Cl. RESET/GO 

 pin 11)

also goes high when LANR goes low, which turns 

 off. Q7 and Q6 then turn on, providing

a discharge path for Cl through Ramp Reset Amplifier U2. Test point 3 remains at ground
potential until HSWP again goes high, starting the cycle again.

The Span Width 

 U17 and 

 provide a negative scan ramp to be scaled by the

Integer Number Attenuator. The output of this negative-going ramp is between 0 and -10
V. The amplitude of the ramp is dependent on the span of the instrument. Frequency span

information arrives on the Instrument Bus and is stored in registers 

 and U18. This

information is clocked into Frequency Span registers U16 and U18 whenever control line LSAS

(Low = Scan Attenuator Strobe) goes low.

The Integer Number Attenuator scales the negative ramp at TP5 to the harmonic band being
swept. This division is by 

 for Band C, 

 for Band D, and 

 for Band E. In Band B,

the ramp is not scaled so it remains unchanged.

The division is performed by R48 through R50. If in Band B, only R80 is in the circuit. In
Band C, R81 is added. In Band D, R82 is added. In Band E, R83 is added. These resistors
are switched in by transistors Q15, Q13, and Q14, which are driven by drivers 

 

and 

 respectively. The information necessary to determine when and which resistors to

switch in comes form the Al2 Front-Panel Interface (SAT 1 and SAT 2) and is decided by
Band Decoder P.

The AUX OUT signal is a positive-going ramp voltage from the scan generator which is
amplified by 

 This output is always 0 to 

 V regardless of the selected frequency span.

If more than one harmonic band is swept, there is a small ramp output from the ramp
generator E (TP3) for each band with each ramp resetting to 0 V. To combine these ramps,
Aux Out Offset DAC U22 and 

 provide a voltage to hold the Aux Out Amplifier input at

a dc level at the end of each ramp. The output therefore is a continuous ramp voltage from
0 to 

 V. This voltage is programmed into the DAC U22 by the span information from

the Instrument Bus. This information is stored in Aux Out Register U23 and U21, being
clocked in by control line LAOS (Low = Aux Out Strobe). This control line is from the Al2

2   A l 6