3 Replies Latest reply on Nov 4, 2011 5:23 AM by gautamd_

    Mixer Component Variable Frequency LO



      I am trying to use the mixer component in PSoC Creator for a project where I need the mixer to have its Local Oscillator sweeping across a wide range of frequencies. I have already developed a varying frequency signal within PSoC, but now I am not sure if I can input this signal into the mixer as the LO for the mixer. It seems to me that the LO to the mixer only accepts a fixed frequency signal at each moment. Am I correct in this assumption? Please help.

        • 1. Re: Mixer Component Variable Frequency LO

          Hi Liberty,




          In which mode are you using the Mixer component? In Down Sampler mode or Up (Multiplier) mode?




          If you using it in Multiplier mode, then during the high period of LO, the input signal will be passed with a gain of (+1) about Vref, and during the low period of LO, the input signal will be passed with a gain of (-1) about Vref.


          Variation in the frequency should not be a problem till it is within the max frequency specified.




          Down mixer acts like a sample and hold circuit. When a LO with varying frequency is given, the Input signal will always be sampled on the rising / falling edge of the LO.

          • 2. Re: Mixer Component Variable Frequency LO

            Thanks for the reply. I just need you to clarify two issues....


            1. So, if I'm getting you right, as long as my LO frequency lies below the setting that I set as my LO frequency during configuration of the mixer component the mixer can work with a variable frequency input at its LO? (I plan to set it into internal LO mode and supply the LO signal internally from within the PSoC)


            2. This LO signal that I supply to the mixer. Can it be any type of analogue wave or does it necessarily have to be a square wave? (I'm thinking of inputting a sine wave signal)



            • 3. Re: Mixer Component Variable Frequency LO

              Hi Liberty,




              1) If you choose the "LO Frequency Setup" as "Internal LO", then the terminal for Local Oscillator (LO) is no longer available on the Mixer Component and it uses the LO of frequency which you enter in kHz.


              If you choose "External LO", then you can choose the local oscillator to be:


              a) Internal to PSoC, such as a clock componentor a PWM component etc




              b) External to PSoC, such as an external square wave.




              In either case, the the clock frequency applied to the LO can be varied. However, it is important to know what is the range of the variable frequency which you would apply to the LO.


              Internally, the Mixer uses resistor value (for the SC/CT block) depending upon the Input impedence Vs slew rate trade off. For LO frequencies less than 100 kHz, the resistor value is selected such that the input impedence is higher. For LO frequencies greater than 100 kHz, the resistor value is selected such that the input impedance is lesser and the slew rate is increased. The decision to use the appropriate value of Resistor is made taking into consideration the LO Frequency entered in the configuration window.




              In your application, if the frequencies are either below 100 kHz or above 100 kHz, then you can choose appropriate value in the frequency tab so that the appropriate value is selected by Creator.




              2) You can use only a Digital signal (clock) for Local Oscillator. You cannot use an analog signal such as sine wave for this.