Zotino as frequency generator in kHz- regime

Hello, maybe one of you has an idea about the following topic. We want to use the Zotino as a frequency generator in the kilohertz range. For this we set a periodeic output of 1V with duration t. Between the pulses there is a delay also of t (see attached script). We now notice that the amplitude of the output signal decreases for higher frequencies (also in the attached folder).
Why is this the case?

`

class DMAPulseZotino(EnvExperiment):
    """
    Record a sequence set for the sinara zotino (two pulses with amplitude 0
    and 1). The script can be used to create a alternating output signal. The
    signal frequency depends on the delay between both outputs. The maximal
    frequency is around 200 kHz for a delay near 1.6 us.
    """

    def build(self):
        self.setattr_device("core")
        self.setattr_device("core_dma")
        self.setattr_device("zotino0")
        self.setattr_argument("time", NumberValue(default=100))

    @kernel
    def record(self):
        """
        Record the sequene set.

        Returns
        -------
        None.

        """
        time = self.time
        volt0 = self.zotino0.voltage_to_mu(0)
        volt1 = self.zotino0.voltage_to_mu(1)
        

        with self.core_dma.record("pulses"):
            for i in range(500):
                self.zotino0.set_dac_mu([volt0], [0])
                delay(time*us)  # minimum for signal is 1.5*us
                self.zotino0.set_dac_mu([volt1],[0])
                delay(time *us)

    @kernel
    def run(self):
        """
        Reset the core device, load the pre-defined sequence set and play this
        set.

        Returns
        -------
        None.

        """
        self.core.reset()
        self.zotino0.init()
        delay(10*us)
        self.record()
        
        pulse_handle = self.core_dma.get_handle("pulses")
        self.core.break_realtime()
        
        while True:
            self.core_dma.playback_handle(pulse_handle)

`