+ Post New Thread
Results 1 to 10 of 10

10th February 2020, 13:42 #1
 Join Date
 Aug 2011
 Posts
 205
 Helped
 0 / 0
 Points
 2,466
 Level
 11
Interpretation of frequency of VCO
A VCO has a transfer function of 100/s, could this mean, it produces frequency which is 100KHz/V?

Advertisement

10th February 2020, 15:03 #2
 Join Date
 Jan 2019
 Posts
 524
 Helped
 138 / 138
 Points
 2,887
 Level
 12
Re: Interpretation of frequency of VCO
which VCO?
what does the data sheet say?
what do the applicable ap notes say?
there (likely) is at least one ap note with a sample usage. what does that say?

10th February 2020, 22:02 #3
 Join Date
 Nov 2009
 Location
 Italy
 Posts
 1,141
 Helped
 394 / 394
 Points
 8,512
 Level
 22
Re: Interpretation of frequency of VCO
The Laplace model of a vco is given by the expression
Phase/Vin = Gain/s
where "s" is the Laplace operator
then in you case Gain=100. Trasforming into time domain we have dPhase/dt = Gain*Vin that is w = Gain*Vin
in your case:
2*pi*frequency = 100*Vin from which frequency/Vin = 100/(2*pi) = 16 Hz/V

Advertisement

11th February 2020, 03:13 #4
 Join Date
 Aug 2011
 Posts
 205
 Helped
 0 / 0
 Points
 2,466
 Level
 11
Re: Interpretation of frequency of VCO
Hi albbg
Suppose the VCO produces output say 1KHz/V (square wave)and I connect it to a 10 bit counter. Then it would take 1 second for counter to roll off. So the time constant is 1 second in this case. Would the transfer function of the combo not be 1/s in this case?

Advertisement

11th February 2020, 07:47 #5
Awards:
 Join Date
 Apr 2014
 Posts
 16,431
 Helped
 3730 / 3730
 Points
 81,036
 Level
 69
Re: Interpretation of frequency of VCO
Hi.
What you say can be mathematically shown as:
f = 1 / t
or
t = 1 / f
KlausPlease don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.

11th February 2020, 08:08 #6
 Join Date
 Aug 2011
 Posts
 205
 Helped
 0 / 0
 Points
 2,466
 Level
 11
Re: Interpretation of frequency of VCO
Hi KlausST
Are you confirming that the expression 1/s is correct?

11th February 2020, 14:01 #7
 Join Date
 Jan 2008
 Location
 Bochum, Germany
 Posts
 46,155
 Helped
 14036 / 14036
 Points
 264,156
 Level
 100
Re: Interpretation of frequency of VCO
Would the transfer function of the combo not be 1/s in this case?
Unless you arbitrarily redefine the commonly understood VCO transfer function definition, you should consider what albbg told. The unit is rad/s rather than Hz.

13th February 2020, 03:00 #8
 Join Date
 Aug 2011
 Posts
 205
 Helped
 0 / 0
 Points
 2,466
 Level
 11
Re: Interpretation of frequency of VCO
At this point of view, I was wondering the difference between VFC vs VCO?

Advertisement

13th February 2020, 09:02 #9
 Join Date
 Jan 2008
 Location
 Bochum, Germany
 Posts
 46,155
 Helped
 14036 / 14036
 Points
 264,156
 Level
 100
Re: Interpretation of frequency of VCO
Literally, a VCO is a VFC (voltage to frequency converter) and vice versa. Specifically the term VFC refers to converters with large frequency ratio (e.g. 0 to xx kHz) and high linearity. The frequency ratio of a VCO can range between several 100 ppm (tuned crystal oscillator) to decades (current steered rings oscillator).

13th February 2020, 17:32 #10
 Join Date
 May 2008
 Location
 Germany
 Posts
 5,794
 Helped
 1730 / 1730
 Points
 40,543
 Level
 49
Re: Interpretation of frequency of VCO
When the given expression is really the TRANFER FUNCTION (and not thefrequency with s=seconds), it must be interpreted as the PHASE characteristics.
This is because in a linear PLL model the input and output quantities are given as PHASE values.
In this case, the transfer function is PHI(s)=Ko/s
with Ko=VCO constant given in rad/Vs.
+ Post New Thread
Please login