I'm improving a project containing a PSoC 1, switching to PSoC 5.
The problem is that PSoC 1 has an instrumentation amplifier up to Three Opamp Topology, allowing dynamical changing of the gain (differential gain + conversion gain). This feature allow to make a fine gain control (< 1) and a big gain control (> 1) too.
With PSoC 5 this feature is still not present. I have only Opamps and PGA that I could connect together to obtain the same configuration.
The problem is the dynamically gain control of PGA. I can't get down gain = 1, so this is reduce the performance of my system because I can make a fine gain control.
Is there a similar PSoC 1 component to use with PSoC 5 or alternatively do you have a solution?
Solved! Go to Solution.
Mainly I need the possibility to make a fine gain control between 0.8 and 1.2 after a big gain control (in step x2 for example 2,4,8,16 etc)..
I have to convert signals from a magnetoresistance into a 1Vpp signals so, if I set the gain to 8 or 16 lead my output signal to going out specifications. I can adjust my gain of 8 or 16 with another gain control between 0.8 to 1.2..
I already thought to place external resistors but I'm using PSoC 5LP in QFN68 where almost all pin are used. Even if I should have the available pins to create a resistors array, I should evaluate if my electronics board has the necessary space.
Furthermore, I'm using a double magnetic resistance so I need to amplifier two couple of differential signals, so I should place a double array of resistors.
After the amplification, my signals going out from PSoC 5 sourcing an external differential driver where I must have the correct amplitude of 1Vpp.
Can you confirm that no more exist internal in the PSoC 5 a component that manage a fine gain control?
Thanks and regards
Depending on the required frequency / response time / precision
Can you use a DAC to output the 1V p-p value per software gain calculation?
Just my two cents
unfortunately I can't use a DAC because the final user takes the 1Vpp signals and use it to interpolate to increase the resolution of the system (he could divide the analog signals up to 2000), so these signals have to be very accurate.
The actually project with PSoC 1 works fine cause we can calibrate a big gain and also a fine gain.
I think that maybe the only way to solve this problem is to use only the big gain control by means of PGA and change the power supply dynamically to the MR (with a PWM) in order to changing the amplitude of the original signals..
could you confirm that in PSoC 5 the SAR ADCs have internal S&H?
My goal is to implement two ADC SAR channel to read analog values from the double MR (see above).
I have to set the two SAR to 1MSPS and when they going to receive a hw trigger, they start to convert (1 conversion each trigger on "soc" pin).
The trigger lets start converting both channel at the same time because the two values are to be used to interpolate sin/cos.
I can't use dedicate S&H component because I used all 4 SC/CT blocks to create two InsAmp, but if I well understood, the SAR has internal S&H, isn't it?
Yes, there is an internal S&H, but it samples only the current channel. The eoc signal indicates when the sampling phase is over and the input can be switched to the next channel.
Here is a "trick" to overcome that situation.
do you mean that there's only one S&H for both two SAR ADC or each SAR ADC has an internal S&H ?
In my device I've got two SAR ADC and I'm going to use both of them (one channel for each ADC), so if each ADC has an internal S&H, I can command both "soc" pin with the same signal to start one conversion at the same time.
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Of course there is a S&H for each SAR ADC 😉
Well, most of your pins are locked. I unlocked all of them and built the project without errors. Just let the fitter do its work...
Locked pins will not be changed by the fitter. When making a pcb it would be fatal when pins change.
Do not forget after a successful build to lock the pins or they might change with every new build.