The enable for monostable A7b is generated by the LLD DISCriminator setting flip
flop A6b/A6c. At the conclusion of the SCA OUTPUT pulse, flip flop A6b/A6c is
cleared via A8a and Ab. If the AMP OUTPUT pulse, exceeds the ULD reference volt-
age, its OUTPUT clears timing monostable (A7a) and flip flop A6b/A6c, terminating
the SCA OUTPUT pulse cycle. The SCA OUTPUT driver provides the additional
drive capability required for driving 50 ohm terminated lines. The SCA OUTPUT
pulse is connected to the front and rear panel BNC connectors, J2 and J103 respec-
tively, through 47 ohm resistors.
Monostable A11b is triggered by the LLD or ULD DISCriminators, selected by J7, pro-
viding the respective OUTPUT DISC pulse at BNC J104. With the aid of jumper plugs
J8and J5, the rear panel DISC BNC (J104)can also be used as an LLD sweep input.
The timing monostable trigger pulse, OUTPUT of A8c or A6a, also triggers mono-
stable Alla providing a drive signal for LED DS1. LED DS1 is provided asa visual aid
for setting the LOWER LEVEL (E) control.
Description of Circuit
Gain Amplifier
Most of the gain (K1 and K2) is accomplished before the integration occurs. As a re-
sult the input amplifier K1 is the dominant noise source. Each of the two gain stages
operate at relatively low closed loop gains providing stable operation with time and
temperature.
Amplifiers K1 (Q14 through Q19) and K2 (Q8 through Q13) are both basically the
same configuration. Therefore only K1 will be fully described.
The differential input pair Q19 drives the common base transistors Q18 and Q15.
Transistors Q18 and 015 operate at low current levels, providing a high OUTPUT im-
pedance to drive the OUTPUT transistors Q17 and Q14 through the common source
FET Q16. The necessary current to drive the FET and circuit capacitance at high fre-
quencies is derived directly from the input transistor Q19, through the low impedance
of Q18 and Q15. This gives a typical slew rate for the amplifier of 140 volts per mi-
crosecond. C12 provides feedback for closed loop stability, and allows the amplifier to
follow a 100 nanosecond rise time input signal with very low distortion. Since the gain
amplifiers do not require dc stability and are operated as inverting amplifiers, a con-
stant current source is not needed in the emitters of Q19. Transistors Q17 and Q14 are
biased on by R30 and R33, with the junction of R31 and R32 providing the low im -
pedance OUTPUT.
31
Description of Circuit
Summary of Contents for 2015A
Page 1: ...Model 2015A Spectroscopy Amplifier Timing SCA User s Manual 9231694B 01 05...
Page 6: ...Notes iv...
Page 12: ...Internal Controls 6 Controls and Connectors Figure 4 Internal Controls...
Page 55: ......
Page 56: ......
