Dc Offset For Positive Pulse Outputs; Step Attenuator; Power Supplies - HP 8082A Operating And Service Manual

OUTPUT
figure 4-8. Input Stage and Attenuator
4 - 4 2
The input signal controls the share of cur-
rent f which flows through each input transistor.
elements Suppose that VCONTRDL sets an attenuation
factor of 2:l and (for simplicity) I = 1mA. !f the INPUT
is such that I is shared equally then 11 = 0.5mA and
ges the sharing of current I so that I1 = 0.2mA and
both cases the sum fx + Ix' = 0.5mA or Jx + lx' = k (con-
stant). This is true for all INPUT current sharing and
attenuation ratios. Therefore, a constant current source
(derived from the amplitude vernier control) can be used
to supply Ix + Ix'. This is shown in figure 4-9.
CONTROL
AMPLITUDE
V E R N I E R
Figure 4-9. Attenuator and Gain Control
OUTPUT
INPUT
4 - 4 3
An advantage of being able to use the one
supply both elements of each attenua-
current source to
tor that the relationship of input control
is
output (signal) current is essentially linear but a slight
non linearity is due to emitter-bulk resistances and
and must be compensated for. This is done %y a seg
Sheet 3b) and the three sets of attenuating
differential amplifier in
4 - 4 4
PULSE OUTPUTS
4 - 4 5
The signal levels from the Ourput
need to be level shifted from negative to positive if posi-
tive pulse outputs are required. This is achieved by the
Positive Pulse DC Offset circuits (one for each channel
switch is set to PDS, two actions occur, the normal/corn
plement relationship of the signals is switched in the
Buffer Amplifier and the Positive Pulse DC Offset
circuit is switched on to raise the signal levels from
negative to positive.

STEP ATTENUATOR

4-46
4-47
The amplitude of the output pulses is con-
trolled by a Step Attenuator (one for each channel
different combinations of attenuators via a diode matrix.
Attenuators used provide 8dB (voltage f 2.5) and 14dB
(voltage + 5) of attenuation.
EXTERNAL DC OFFSET
4-48
The output pulse baseline can be adjusted
4 - 4 9
over the range -2V to +2V using the External DC Offset
circuit (Service Sheet 3b). Both output
controlled by a common vernier and the circuit can
also be switched off in which case the pulse baselines
are at OV.
POWER SUPPLlES
The power supplies (Service Sheet 5)
4-51
four separate power rails, +lOV,
provide
-25V. Each supply is regulated and protected against
short circuits. The output voltages can be adjusted using
variable resistors R7 (+lOV), RlO (-5V), R21 (-lOV),
supplies incorporate current fold-back regulation which
makes them self-starting after short chcuits.
to
Amplifier