Signal Conditioning Made Easy with X-FAB
X-FAB is enabling best-in-class low noise, highly sensitive and linear signal conditioning circuits with analog or digital interfaces. Its CMOS processes are optimized for best 1/f noise performance, come with excellent matching properties and optimized capacitors. Those capacitors feature low-volage coefficients, low temperature dependancy and high unit capacitance per area. In addition, bipolar processes are also available.
Signal Conditioning IC - Block Diagram
The sensor bridge is biased by a constant current source CSOURCE. The outputs of the sensor bridge are connected to the differential inputs P and N of the Programmable Gain Amplifier (PGA). Based on the temperature measured by the temperature sensor TEMP and the correction factors stored in the non-volatile memory (NVM) for this temperature, the gain of the PGA is controlled. This way, the temperature dependency of the sensor characteristics is taken into account. The analog output signal AOUT of the PGA is fed into a precision analog-to-digital converter, and is converted into digital pattern available at the output DOUT of the chip.
The sensor, which is shown here as an external sensor element in bridge configuration, can be external or internal. Hall CMOS sensors, optical CMOS sensors and MEMS based sensors are offered in various X-FAB process technologies for direct integration with the CMOS signal conditioning circuitry and other parts of the system.
Programmable Gain Amplifier (PGA)
The Programmable Gain Amplifier (PGA) amplifies the differential sensor input signal with a gain defined by digital data applied to the programming inputs of the block. By varying the gain the signal conditioner is able to overcome non-linearities of the sensor element and the temperature dependency of some of its parameters like offset and sensitivity.
The required design parameters of PGA strongly depend on the type of the sensor. Whereas for inductive sensors the task would be to cope with rather large signals which need to be clamped by the input circuitry of the PGA, in most cases (Hall, optical, MEMS) the problem is the opposite, that is, the sensor output signal is very low and very close to the noise floor achievable. X-FAB technologies offer a comprehensive variety of analog primitives with outstanding noise and matching behavior. Precise device models with noise and matching accurately modelled, statistical data and process monitoring enable results with high performance and yield.
Analog-to-Digital Converter (ADC)
Depending on requirements Analog Digital Converters can be designed by using the standard core or additional modules for reduced noise, trimming devices or memory. Use of junction isolated devices makes the ADC design robust versus substrate noise.
Zener zaps and fuses are available for trimming of parameters like offset during wafer probing or final test.
Several robust ADCs can be selected from X-FAB's analog standard cell library.
This non-volatile memory block stores temperature correction factors that are sensor specific, like sensitivity, linearity and offset. X-FAB offers a process dependent portfolio of embedded NVM IP like ROM, OTP, EEPROM, FLASH and NVRAM. If a programmable NVM is used, the sensor conditioner could be designed to fit a variety of sensor types. Before actual use it would get programmed according to the specific parameters of the sensor used.
Depending on the requirements the analog-to-digital converters is designed by using the standard core or additional modules for low noise and trimming devices.
The use of junction isolated devices makes the ADC design robust to substrate noise.
Zener zaps and fuses are available for trimming of parameters like offset and would be programmed during wafer probing or final test.