Tag Archive for Analog

Keysight N7020A 2.0GHz Power Rail Probe Review, Teardown and Experiments

N7020A

In this episode Shahriar reviews the Keysight N7020A 2.0GHz Power Rail Probe. This power rail probe boasts the following features:

  • Low noise: 1:1 attenuation ratio probe adds only 10% to the baseline noise of the oscilloscope it is attached to.
  • Large offset range: Has a large +/-24 V offset range, enabling users to set their oscilloscope at maximum sensitivity and have the signal centered on the screen.
  • Low DC loading: 50 kΩ DC input impedance will not significantly load DC power rails.
  • Large active signal range: Has a +/-850 mV active signal range in addition to its large offset range so users can measure large transitions of their power rails.
  • High bandwidth: 2-GHz bandwidth makes it very useful for finding high-speed transients that can have detrimental effects on clocks and digital data.

After a brief presentation about the benefits of the N7020A, the probe and probe accessories are examined. The probe’s capability to provide up to +/-24V of offset is demonstrated and the input impedance at DC is measured. The probe is then used in conjunction with a Xilinx FPGA board to characterize a broadband power supply noise issue.

Teardown and Repair of a Fluke PM6303A Automatic RCL Meter

PM6303A

In this episode Shahriar examines a faulty Fluke PM6303A Automatic RCL Meter. This unit power on however reports the incorrect measured value for all components. The instrument also does not provide the built-in 2V bias. After a quick teardown of the unit, physical damage to several input resistors can be observed. It becomes clear that a high-voltage discharge has caused a cascade failure of several components on the input signal path. These faults are traced to a chain of protection Zener diodes, resistors and general purpose diodes. After all the components have been replaced, the unit’s functionality is restored.

The schematic and block diagram of the unit is also presented and the principle of operation is explained. The repaired instrument is then used to measure several components to verify is functionality.

Teardown, Repair & Calibration of a Fluke PM6680B 225MHz High Resolution Frequency Counter

PM6680B

In this episode Shahriar repairs a Fluke PM6680B 225MHz High Resolution Frequency Counter. This unit which is equipped with a soft power button, does not power on. The standby LED is dimly lit and a high-frequency noise is emitted from the unit. This points to a switching power supply failure. The power supply is a simple fly-back converter with three outputs (5V, 18V, -8V). The 5V output is regulated while the other two outputs are single diode rectified.

The fault is traced to a bad precision reference IC which is replaced. The performance of the power supply is verified and the instrument powers on. An OCXO is used to calibrate the 10MHz reference crystal of the unit after the repair is completed.

Teardown, Repair & Calibration of a Valhalla 2701C Programmable Precision DC Voltage Standard

2701C

In this episode Shahriar examines a faulty Valhalla 2701C Programmable Precision DC Reference instrument. Valhalla Scientific’s 2701C Programmable Precision DC Voltage Calibrator delivers ultra-precision, ultra-stable DC voltage from 100 nanovolts to 1200 volts. This unit does not have a working front-panel LCD screen. Luckily, that problem is resolved very quickly.

The internal build and operation of the unit is briefly examined and the instrument is calibrated using a Keithley DMM7510 7.5-digit multimeter. It is possible to upgrade this unit to a more stable and accurate reference voltage generator or to add the reference current capability to it.

Tutorial on the Theory, Design and Characterization of a CMOS Transimpedance Amplifier

TIA

In this episode, Shahriar and Shayan discuss the design and characterization of a deceptively simple CMOS inverter-based transimpedance amplifier. The the large and small signal behavior of the CMOS inverter is discussed and measured using the Keithley 2450 and 2460 source meters. The transient response is also measured using a Keysight MSO-S series oscilloscope.

The small signal gain of the circuit is calculated from small signal parameters which are extracted directly by measuring the devices I/V characteristics. The NMOS/PMOS devices used are from an ADL1105 quad-discrete transistor IC. Through the use of a shunt-shunt feedback, the CMOS amplifiers is converted to a transimpedance amplifier which is capable of amplifying the current from a photo-detector diode by a gain of 30kV/A. The feedback theory is used to calculate the gain of the amplifier. The slides for this tutorial can be downloaded here.

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