Trans-Impedance Amplifier For for Physics Experiments

High bandwidth TIA

In this project a trans-impedance amplifier TIA with a nominal bandwidth of 1 GHz, a nominal gain of 70 dBOhm, and an input impedance of < 30 Ohm is implemented. The nominal operating voltage is 1.8 V. The output has a nominal impedance of 50 Ohm and is differentially intended to drive a load with a capacitance of up to 10 pF.

The TIA design is based on [1]. It is augmented by an on-chip reference current source for biasing based on [2]. Finally, a 50 Ohm differential output driver is implemented. For electrostatic discharge (ESD) protection clamping diodes are used.

The circuit is intended for use as a preamplifier for characterizing SiC PIN diodes. However, it can find wider use, e.g. in optical communication and in physics experiments. The differential output is intended to be attached to an external high-speed ADC or oscilloscope.

Reference current source

Post-layout simulations reveal a precision of the current source of +/-10% as shown below. The output of the current source is provided on an analog output via a current mirror for characterization.

TIA

Simulations show that the bandwidth of the TIA is between 0.9 and 1.8 GHz depending on the temperature and process variations. However, this bandwidth is not available at the output. It is merely relevant if the TIA is reused in a design where the output is directly processed within the chip. The Gain is between 54 and 60 dBOhm, again this signal is not available at the output of the chip. Please refer to the section Output for details on the output characteristics.

Output driver

The output driver is intended to complement the TIA. Into a 10pF load capacitor, it delivers a bandwidth of 0.8GHz or more, depending on the temperature and process variations.

Organization of files

TIA:

• xschem/tia/tia_rgc_core.sch contains the TIA.
• mag/tia/core/tia_core.mag contains the layout
• xschem/test/test_tia_rgc_full.sch can be used to testing modifications of the TIA
• xschem/test/test_tia_rgc_full_mc.sch is intended to check the impact of temperature and process variations on the performance.

Output driver:

• xschem/outdriver/outdriver.sch contains the circuit
• mag/outd/outd.mag contains the layout
• xschem/test/test_outd.sch is used for testing modifications to the output driver

Low PVT current source:

• xschem/bias/low_pvt_source.sch contains the circuit
• mag/isource/isource.mag contains the layout
• xschem/test/test_tia_rgc_full.sch is used for testing modifications
• xschem/test/test_tia_rgc_full_mc.sch is intended to check the impact of temperature and process variations on the performance.

Integration testing:

• xschem/test/test_tia_rgc_integration.sch tests the interplay between all components.
• xschem/test/test_tia_rgc_integration_mc.sch is intended to check the impact of temperature and process variations on the performance.

Links:

• EFablesss MPW-5 Project: https://platform.efabless.com/projects/730
• Github Repo: https://github.com/Unkraut3/caravel_tia

This project was created by Unkraut3, and we are sharing it here to help spread the word about the EFabless Open MPW Shuttle Program.