How do I normalize amplitude of a sine wave to 1V p-p? - Page 1
Forum section: electronics / projects

author: hkBattousai
author_rank: Regular Contributor
timestamp: August 09, 2014, 02:16:15 pm
content: I need to normalize amplitude of a given sine wave to a fixed value to be used as a reference signal in the succeeding circuit blocks. It will correspond to the red block in the block diagram below. How do I implement it?

author: Jebnor
author_rank: Regular Contributor
timestamp: August 09, 2014, 04:25:29 pm
content: 12Vpp input... 1Vpp output... A divide by 12 Resistor divider?

author: PChi
author_rank: Frequent Contributor
timestamp: August 09, 2014, 04:31:15 pm
content: I am not sure if I uderstand what the red block needs to do.A multilplier like the Analog Devices AD633 can scale a sine wave. But it needs a voltage to control the gain which could be from an error amplifier comparing the output of the Precision rectifier circuit after averaging with a DC reference.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 09, 2014, 04:39:29 pm
content: This is the entire feedback loop...?How does a comparator make a PWM sine wave from gibberish?Tim

author: jpb
author_rank: Super Contributor
timestamp: August 09, 2014, 04:48:21 pm
content: Are you sure you've drawn the circuit as you want it? If the red block is acting as a reference then why does it need an input?If it is just to set the level for the comparator why use a precision rectifier? Why not just have a dc voltage reference set to the peak value (1V) and a peak detect after the Divide by 12. Or you could use a 12V reference perhaps.I'm suggesting the peak (or peak minus a diode drop) as the rectified value might change with frequency - if the filter means that the frequency is constant then you could just use a rectified value.With the circuit as drawn it looks like you'd need a reference of some sort to set the 1V reference which would defeat the point of it.

author: hkBattousai
author_rank: Regular Contributor
timestamp: August 09, 2014, 05:05:20 pm
content: Quote from: T3sl4co1l on August 09, 2014, 04:39:29 pmThe main sinusoidal signal source is a separate oscillator inside the "PWM Generator" block which is not explicitly shown in the block diagram.Quote from: jpb on August 09, 2014, 04:48:21 pmBut the sinusoidal reaches its positive peak value only once in a period. I want to have immediate control over it.

author: IanB
author_rank: Super Contributor
timestamp: August 09, 2014, 05:10:34 pm
content: Quote from: hkBattousai on August 09, 2014, 05:05:20 pmTo measure the amplitude you have to wait for one complete period and look at the difference between the maximum and minimum voltage values. No?

author: dannyf
author_rank: Super Contributor
timestamp: August 09, 2014, 05:12:02 pm
content: AGC.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 09, 2014, 05:18:30 pm
content: Quote from: hkBattousai on August 09, 2014, 05:05:20 pmCan you please redraw the diagram so it is in terms of real time-domain voltage signals?Tim

author: zapta
author_rank: Super Contributor
timestamp: August 09, 2014, 05:19:51 pm
content: Quote from: hkBattousai on August 09, 2014, 02:16:15 pmThe four green blocks on the right are clear. The ones on the left to the comparator are not. Can you when do you want to enable the PWM and when to want to disable it?

author: David Hess
author_rank: Super Contributor
timestamp: August 09, 2014, 05:41:52 pm
content: It is not clear to me what you are trying to do but there are a variety of analog variable gain circuits which can be used with a detector and integrator to level a sine wave or other waveform. At low frequencies, closed loop detectors can be used for high accuracy but at high frequencies, temperature compensated open loop detectors are used.

author: AlfBaz
author_rank: Super Contributor
timestamp: August 10, 2014, 09:36:23 am
content: If all you want from the signal is its frequency/phase how about a PLL?

author: penfold
author_rank: Frequent Contributor
timestamp: August 10, 2014, 10:03:08 am
content: +1 for automatic gain control.However, I'd be a touch wary of automatic gain controllers common to the stabilisation of radio reception, audio etc because their transient response is normally very slow. As far as putting a classic AGC into a closed loop system, there's a number of problems because it would basically be non-linear and intrinsically low time constant during any transient event. There are some clever things that can be done digitally to get the gain controller to respond before a fraction of the first sine wave has elapsed. But that all depends on the final application.

author: dannyf
author_rank: Super Contributor
timestamp: August 10, 2014, 02:31:00 pm
content: QuoteAll true.However, the original block diagram actually makes little sense. If the OP is looking for a constant 12vpp output, all s/he needs to do is to apply a 1v voltage to the comparator's non-inverting input.

author: edavid
author_rank: Super Contributor
timestamp: August 10, 2014, 05:58:57 pm
content: Check out this app note for a fancy Jim Williams circuit (Figure 20):http://cds.linear.com/docs/en/application-note/an106f.pdfYou could replace the RMS converter with a simpler detector to save money.

author: David Hess
author_rank: Super Contributor
timestamp: August 10, 2014, 08:52:58 pm
content: Page 64 of application note 47 and page 13 of application note 52 show exactly that with the RMS converter replaced with a temperature compensated diode detector.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 10, 2014, 09:05:01 pm
content: Hi group,Detectors and rectifiers are normally used in high Frequency or RF circuits.The system requirements could probably met by using a Class D audio amplifier. The Class D amplifier would contain a feedback loop to regulate the instantaneous value of the output voltage. If the instantaneous value is corrected by the feedback loop the RMS and peak values will take care of themselves.A precision AC reference can be made by clocking sine wave data into a DAC.The original poster does not give the frequency or accuracy requirements for the system.Regards,Jay_Diddy_B