BNC PB-5 - Manual (Page 3)

2
SECTION 1
OPERATIONS
1.1 INTRODUCTION
The PB-5 sets a new standard for nuclear pulse generators. It offers full digital
controllability with a built-in ramp generator. It provides tail and flat top pulses with
excellent integral linearity and extremely low amplitude change with temperature. The
PB-5 is capable of testing the stability, linearity and resolution of the most demanding
spectroscopy circuits and instrumentation. It is the successor to the industry standard
PB-4.
The PB-5 programmable precision pulse generator is menu-driven utilizing a 16-bit
microcontroller. The front panel consists of a LCD display, keypad, and a spinner knob
for selection of parameters and fine adjustments. A precision 16-bit DAC in conjunction
with a 10-bit trim DAC is used to obtain excellent linearity and resolution over the 0 to
10 volt range. When driving 50
loads the output range is 0 to 5 volts (without
affecting stability, linearity, or pulse shape). Temperature compensation is performed
with an algorithm in software allowing precision (16-bit) settings and repeatability
within ± 5 ppm/C
° . Digital control is either manual or by RS-232 interface. Menu
selections, such as saving/recalling pre-programmed configurations, provide many new
features not previously available. The PB-5 will not require a separate ramp generator
for linearity tests since it produces a digitally controlled linear ramp that will accurately
test large multi-channel analyzers.
1.2 PRINCIPLES OF OPERATION
The block diagram is shown in Figure 1. A microcontroller (µC) and its flash memory
control the PB-5. The µC receives external input commands from the keypad, spinner
selector knob, RS-232 port, and temperature sensor readings. The µC then converts
these inputs to various codes that in turn drive the selected functions. When the unit is
turned off the µC stores the last settings of the pulser so that these settings can be
recovered upon powering up the unit. It has the capability of storing an additional nine
pulse settings for recall at any time. The amplitude is generated by a 16-bit serial DAC.
The pulse is created by an electronic switch within the Pulse Amplitude circuitry. Next
the pulse is shaped and fed to the Attenuator control which has a 50
series terminated
output. The pulse parameters are shown to the user on a LCD display. These
parameters are set by the keypad or by the spinner knob (optical encoder). The spinner
has a push switch for enabling and selecting the user values. The spinner performs the
same functions as the keypad but it is much easier to use. The keypad on the other hand
allows a precise setting to be entered (e.g., amplitude 1.256750 volts for precision and
repeatability).
The External Pulse Input passes through a limiter circuit and an adjustable level
discriminator. The Input discriminator is controlled by a 10-bit serial DAC.