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


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.

Tutorial and Experiments with ESP8266 SoC, Blynk App, Arduino and Internet of Things (IoT)


In this episode Shahriar explores the functionality of the popular ESP8266 SoC chip. This IC incorporates a full ISM radio as well as the physical/MAC layer for 802.11b/g/n network communication. Furthermore it includes a uC core for code execution making it a low-cost candidate for Internet of Thing applications. This video uses a Sparkfun Thing evaluation board which also includes a LiPo batter charger, voltage regular, flash memory and all the I/O pins which are accessible to the user. The block diagram of the ESP8266 is reviewed as well as the schematic of the complete Sparkfun Thing board.

By using an Arduino library and the Blynk iOS application, a cell phone and the ESP8266 can simultaneously communicate with a server running the Blynk application and transfer data between the application and the module. In this demo various components such as NeoPixel (WS2812), OneWire temperature sensor and battery monitoring functionality are implemented. The code is available here.

Rigol DSA875-TG 9kHz – 7.5GHz Spectrum Analyzer & Tracking Generator Review, Teardown & Experiments


In this episode Shahriar takes a close look at the top-of-the-line Rigol DSA875-TG 7.5GHz Spectrum Analyzer. This unit which, offers a built in tracking generator for the full frequency range, has a portable form-factor. I offers the following performance:

  • 9 kHz to 7.5 GHz Frequency Range
  • Typical -161 dBm Displayed Average Noise Level (DANL) normalized to 1 Hz
  • -98 dBc/Hz @10 kHz offset Phase Noise
  • Total Amplitude Uncertainty <0.8 dB
  • 10 Hz Minimum Resolution Bandwidth (RBW)

The unit is tested against linearity specification as well as overload conditions. The phase noise of the unit is also verified with an external Keysight synthesizer. The instrument is used to measure OIP3, P1dB input and output matching of various amplifiers. The tracking generator is also used to measure gain and switching behavior of a WiFi extender module. The built-in functions are used to measure OBW, channel power, ACP and THD. The teardown of the unit is also presented showing excellent build quality and manufacturing.

Repair of PXI-2596 (Microwave Switch), PXI-4461 (Signal Analyzer) & PXI-4071 (7.5 Digit FlexDMM)


In this episode, Shahriar repairs a few PXI module cards including a PXI-2596 Microwave Switch, a PXI-4461 Signal Analyzer and a PXI-4071 7.5 Digit FlexDMM unit. The PXI-2596 and PXI-4461 have both suffered mechanical damage to the on-board components. Some re-wiring as well as component replacement is necessary to correct the problems.

The PXI-4071 module halts the PXI system boot up entirely. The card is missing a flash memory IC and could potentially have a bad PXI bus main IC. The PXI bus IC replacement does not correct the problem. This implies a missing firmware on the flash memory IC.

Teardown & Repair of a Matsusada RE-600-1.6 600V 1.6A Power Supply


In this episode Shahriar attempts the repair of a Matsusada RE-600-1.6V 1.6A power supply. This low profile power supply is intended for rack-mount application and has been likely used in a vapor deposition system before it has failed. The scent from the unit hints at capacitor failures due to thermal stress over a long period of time. The teardown of the unit reveals the low-profile construction as well as the ventilation air flow. The faulty capacitors are replaced with higher temperature rated units. Unfortunately further faults are detected and it is revealed that the main switching transistors have also failed. All part number of all ICs and control modules are either sanded off, or permanently potted. Since no schematic is available, the repair has to be temporarily put on hold.

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