Phase/Frequency Modulators

1 / 6

# Phase/Frequency Modulators - PowerPoint PPT Presentation

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”.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

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.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

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

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)

“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

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

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

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