1 / 6

Phase/Frequency Modulators

Phase/Frequency Modulators. Frequency Modulation using a Voltage Controlled Oscillator (VCO). v o (t) = V c cos{2 p [f c +k 0 v m (t)]t} k 0 v m (t) = D f(t). f out. f c , k o (Hz/v) VCO. v m (t). “Modulation Sensitivity”.

Download Presentation

Phase/Frequency Modulators

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Phase/Frequency Modulators Frequency Modulation using a Voltage Controlled Oscillator (VCO) vo(t) = Vccos{2p[fc +k0vm(t)]t} k0vm(t) = Df(t) fout fc , ko(Hz/v) VCO vm(t) “Modulation Sensitivity” This is the only parameter we are interested in! Not the frequency, not the voltage, but the Frequency Deviation. This is the parameter that represents the source information signal; and this is what we recover during demodulation. fout fc ko “Free Running Frequency” frequency of operation when input voltage is zero. Df(t) fout(t) vm(t) k0 vm + fc

  2. Phase/Frequency Modulators Reference Phase Phase Modulation using a Voltage Controlled Phase Shift fc vo(t) = Vccos{2pfct+kpvm(t)} kpvm(t) = F(t) vm(t) kp(rad/v) “Modulation Sensitivity” Phase Deviation F This is the only parameter we are interested in! Not the frequency, not the voltage, but the Phase Deviation. This is the parameter that represents the source information signal; and this is what we recover during demodulation. vm

  3. Determining Modulation Sensitivity for a Phase Modulator Reference Phase V(t)=I0ZT(t)) = V ejq(t) = V ej(wt+F(t)) i(t)=I0cos(wct) Phase Deviation

  4. Chain Rule v0 is the DC bias level which gives zero phase shift. When v0 is applied to the diode: C(v0) = C0(1+2v0)-1/2 = Cc w(v0)= wc S(v0) = 0

  5. Varactor Diode Characteristic

  6. Limit of Linearity: How good is good enough? DF s se Phase Error DFe se s For a maximum fractional error (distortion) of e, the maximum normalized frequency displacement is: 1 If e < 0.05, DFMAX < 0.39R

More Related