Microchip Technology 4310B, User Manual

Page: 35 / 49

Theory of Operation
 2021 Microchip Technology Inc. DS50003057A-page 35
FIGURE 5-8: Maximum Signal Level at the Ramsey Interrogation Points.
The optimum microwave power point, designated POPT is indicated in the above
figure. To ensure that the microwave power is always optimized, the CsIII periodically
measures the signal response to small variations of the microwave power, as shown in
the figure, alternately performing the measurement on the left- and right-side clock
Ramsey interrogation points. This response is input to a digital servo, whose output,
the Microwave Power Control Voltage, controls a variable attenuator in the microwave
synthesizer, higher voltages producing lower output power at 9192 MHz. The range of
the Microwave Power Control Voltage is 0V - 5V and the synthesizer is set in the factory
such that POPT is accomplished near to a setting of 2.5V. In normal operation the
Microwave Power Control Voltage may vary from 1.5V to 4V, particularly in response
to changes in ambient temperature.
5.7 UNIT INITIALIZATION
Upon power-up, the CsIII performs the following sequence of operations.
Upon completion of the warm-up sequence, the offset frequency of the instrument is
expected to meet its specified accuracy, though it may continue to move by several
parts in 10
13
over the first several hours of operation as the instrument temperature
equilibrates and the Zeeman, gain, and microwave power servos converge on their
optimum values.
TABLE 5-1: WARM-UP SEQUENCE
Warm-up Sequence Completion Indicator
Firmware and non-volatile RAM consistency
check
RS-232 communication begins
OCXO Oven Warm-up OCXO Oven changes from “cold” to “Ready”
Cesium Oven Warm-up Cesium Oven voltage drops below 10V
Clock Rabi Acquisition Clock Rabi Error <40 mV
Clock Ramsey Acquisition Clock Ramsey Error <40 mV
Gain Servo Initialization Clock Level >2000 mV
Zeeman Rabi Acquisition
Zeeman Rabi Error < 40 mV
Front panel Lock LED illuminates