There are two LPF Blocks available in PSoC 3/5. Each LPF can be tuned by changing the values of Resistor (R) and Capacitor (C). The Resistor value can be selected as 208K ohms or 1.04 M ohms. The Capacitor value can be selected as 5pF or 10pF. Hence four cut-off frequencies are supported by the LPF, that is, 15KHz, 30KHz, 76KHz and 153KHz.
Refer to the figure below which shows the Routing of the analog LPF.
The inputs are selectable in a 2:1 mux for each LPF. On the left side, the LPF inputs are AMUXBUSL and AGL0. On the right side, the inputs are AMUXBUSR and AGR0. The outputs are connected through switches to abusL0 and abusR0, respectively.
Please refer to the Technical reference Manual (TRM) for more details on this block. The TRM can be found at http://www.cypress.com/?id=2232&rtID=117.
The LPF control registers are LPF0_CR0 and LPF1_CR0. The Control register is as shown below:
When csel = 0, C is 5pF
csel = 1, C is 10pF.
When rsel = 0, R is 208k ohm
rsel = 1, R is 1.04M ohm
When swout = 0, LPF output is not connected
swout = 1, LPF output is connected to Analog local bus 0.
When swin = 00, inputs are not connected.
swin = 01, Analog Global 0 is connected (AGL0 o/ AGR0)
swin = 10, Analog Muxbus is connected (AMUXBUSL / AMUXBUSR)
swin = 11, Both Analog Global and Analog Mux are connected.
These filters have only 4 cut-off frequencies. Since it acts as a simple R-C Low pass filter, the impedance matching has to be taken care of.
If you are intending to use this filter, then you'll have to buffer its input / output via an opamp or PGA in voltage follower mode. Else the signal will be attenuated.
Very thanks info about LP filter.
Please is possible make simple working module ? This is very hard for me im dont understand how to use registers.
Many many thanks
As you are not comfortable using registers, it will be easier to use the component to configure and use the LPF.
The schematic will look as shown below:
The LPF's output is buffered via opamp and put out on an analog pin.
Please be aware that this LPF component is just a trial component and is not fully tested. You have choice of four frequencies - 15kHz, 30kHz, 76kHz and 153kHz.
The output impedance of the LPF is high, hence the output should be buffered before bringing it out on a pin.
Many thanks this is very usefull module for me.
You're welcome Kamil.
All the Best!
Estoy haciendo un filtro pasabandas de 4 orden con un Psoc de la familia 1.
No entiendo bien los parámetros de frecuencia central y ancho de banda, tenía mis parámetros de la siguiente manera:
La señal que quiero filtrar está entre 20 Hz y 500 Hz; si sigo la lógica de filtros la frecuencia central está dada por la raíz del producto de éstas dos frecuencias, es decir FC = SQRT(500*200) = 100 Hz; ahora bien, el ancho de banda es la diferencia de las dos frecuencias, es decir BW = 500 - 20 = 480 Hz
Con esta lógica no funciona mi filtro.
Agradecería que me pudieran aclarar o dar un tutorial de cómo calcular bien el ancho de banda y la frecuencia central para ese pasabandas.
RTA_FILTRO_20_500.JPG 71.7 K
Can someone translate this manually, so that no Information gets lost? Bob (small window)
Translated: Hi, I am doing a 4th-order, band pass filter with a PSOC1. I don’t understand well the parameters for the center frequency and bandwidth. I had my parameters like this: The signal I want to filter is between 20 and 500 Hz. If I follow filter logic, the center frequency is given by the root of the product of these two frequencies, in other words FC = SQRT(500*200) = 100 Hz. Also, the bandwidth is the difference of the two frequencies, that is BW = 500 – 20 = 480 Hz. Using this logic my filter does not work. I would appreciate if someone could clear this up for me, or show me a tutorial of how to correctly calculate the bandwith and frequency centerpoint (center frequency) for this band pass filter. Thanks,
What exacly does not work as you expect? Do you have a scope picture? Can you post the complete project here so that we all can have a look at? (Use the Archive function of Designer) Bob (small window)
Would this moved back to PSoC1sub forum?