Keysight Technologies N4000A SNS Series Operating And Service Manual

Contents

4 Operating Guide46 Keysight N4000/1/2A Operating and Service ManualServicePrinciples of operationReferring to the SNS block diagram in Figure 4-13 on page 45, a constant +28 Vis supplied from the NFA through the multi-pin “Connector” block when the SNSis connected to the noise figure analyzer. A voltage inverter is used in the N4000Aand N4001A to input approximately –25 V to the current regulator.The current regulator applies a negative bias current to the noise diode for theN4000A and N4001A models. The N4002A utilizes a positive bias, so the voltageinverter is not necessary. The current regulator block also provides the switchingnecessary to produce the noise “On” and “Off” states.The 2-wire bus interface allows for data transfer to and from the noise source. Thedata stored in the EEPROM includes model, serial number, diode current setting,and SNS calibration data.The power supply provides +5 V to the 2-wire bus interface, EEPROM, and digitaltemperature sensor.The digital temperature sensor is a digital thermometer, thermally coupled to themicrowave assembly.When the smart noise source is in its “On” state, the noise diode producesbroadband noise which is input to the attenuator.The attenuator sets the final Excess Noise Ratio (ENR) and output impedance ofthe smart noise source. A 16 dB attenuator is used in the N4000A to providenominal ENR values of 5 dB. A 6 dB attenuator is used in the N4001A and N4002Amodels for nominal ENR values of 15 dB.The standard output connector is a Precision 3.5 mm. A Type-N connector isoptional.TroubleshootingCheck the connectors and perform the operator’s check described in theOperating Instructions section of this manual. If the operator’s check resultsindicate a problem, or if the connectors are damaged, please contact KeysightTechnologies. Our representatives can help isolate the problem and makearrangements for repairs if necessary.