SineMixer < ColdFeedback

---+ Sine Wave Mixer

The transfer function of a sine wave mixer acting on broadband white noise is 1/sqrt(2). There is a factor of sqrt(2) from adding the left and right sidebands and a factor of 1/2 from the identity:

$\cos \theta \cos \varphi = {{\cos(\theta - \varphi) + \cos(\theta + \varphi)} \over 2}$

The following graphs illustrate my toy simulation to verify this:

Amplitude spectral densities of a unit amplitude broadband white noise timestream, a sine mixer and the product of the two.

Note that at baseband, the mixed signal has a level that is factor of 1/sqrt(2) that of the input broadband signal. In firmware, we remove the factor of 1/2. This means that a demodulated timestream containing white noise needs to be divided by sqrt(2) in order to be referred back to the equivalent broadband noise level.

-- TijmenDeHaan - 2014-02-17

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Topic attachments
I	Attachment	Action	Size	Date	Who	Comment
png	sine_mixer.png	manage	30.7 K	2014-02-17 - 19:49	TijmenDeHaan

This topic: ColdFeedback > WebHome > SineMixer Topic revision: r1 - 2014-02-17 - TijmenDeHaan