Mr
Servando Espejo
(IMSE-CNM-CSIC / Universidad de Sevilla)
The MEDA WS FE ASIC performs two main functions.
On one hand, it contains an instrumentation amplifier and a 16-bits analog to digital converter (ADC) that uses a fully differential dual-slope approach, an analog multiplexer to allow the sequential conversion of 16 analog channels, and some configurable sensor-bias circuitry. This functionality aims to measure temperatures at different points in the instrument using external platinum resistors.
On the other hand, the ASIC includes a number of identical heating currents and temperature control loops used to maintain a constant temperature on external silicon dies that include platinum resistors. The heat power required by each of the dies for this purpose is measured, providing an indirect measure of the wind speed (magnitude and direction).
The ASIC includes a digital finite state machine (FSM) for functions control and data communications with the external control unit. Other secondary functions include internal temperature and power supply monitoring, and authomatic heaters shut-down in the event of overheating of the external dies. A power-on reset circuit has also been included, as well as the required internal voltage and current references.
The die size id 5 x 5 mm approximatelly. The specified operating (ambient) temperature range is -128 to +50 ºC, the maximum ionizing radiation dose is 9Krad, and should be latch-up free up to a LET of 75 MeV-cm2/mg. It should also be robust against SEUs and SETS up to an LET of 37 MeV-cm2/mg.
The controlling FSM operated on a 2.4MHz clock, provided by the external Instrument Control Unit. The communication is based on an UART. Both the external clock and data lines (Rx and Rx) use RS-422 physical layers.
The interna ADC includes its specific controlling FSM that runs on a higher 50MHz internal oscillator.
The ASIC is configurable in many aspects. Configuration registers include parity check for SEUs detection.
It has been packaged in a 100-pins CQFP.
Summary
This paper describes a front-end mixed signal ASIC designed in a standard CMOS 0.35um technology from AMS.
The ASIC has been designed as a component of a wind (magnitude and direction) sensor included in the Mars Environmental Dynamics Analyzer (MEDA), one of the science instruments of the Mars 2020 mission (http://mars.nasa.gov/mars2020/mission/instruments/).
The ASIC has been specified by CRISA (www.crisa.es/) on the basis of a wind-sensor concept provided by UPC (Politechnique University of Catalonia). CRISA has also been in charge of the high-level digital code of the controlling and communication finite-state machine (FSM) included in the ASIC for control and communication with the instrument control unit (ICU).
IMSE-CNM-CSIC has been responsible for the design of the ASIC, including its analog architecture and blocks and the synthesis and back-end of the digital part.
A RH digital cells library, previously designed by IMSE in this technology [1], has been used for the digital sections, while analog section use Enclosed Layout Transistors (ELTs) and ward-rings for radiation hardness.
Mr
Servando Espejo
(IMSE-CNM-CSIC / Universidad de Sevilla)
Mr
Antonio Ragel-Morales
(IMSE-CNM-CSIC)
Mr
Joaquín Ceballos-Cáceres
(IMSE-CNM-CSIC)
Mr
José Miguel Mora-Gutiérrez
(IMSE-CNM-CSIC)
Mr
Juan Ramos Martos
(IMSE-CNM-CSIC)
Mr
Luis Carranza-González
(IMSE-CNM-CSIC)
Mr
Miguel Ángel Lagos-Florido
(IMSE-CNM-CSIC)
Mr
Samuel Sordo-Ibáñez
(IMSE-CNM-CSIC)
