The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Simulators >> Circuit Simulators >> How to simulatue a Gm-C integrator?
https://designers-guide.org/forum/YaBB.pl?num=1141381116

Message started by tumeda on Mar 3^rd, 2006, 2:18am

Title: How to simulatue a Gm-C integrator?
Post by tumeda on Mar 3^rd, 2006, 2:18am

My question is how to extract the nonlinearity of a Gm-C integrator, i.e. THD (total Harmonic Distortion). SNR (Signal-to-Noise Ratio) and SDR (Signal-to-Distortion ratio)?
As my knowledge, these perforamnces are from the FFT of a signal. Does it need a tranisent simulation???

In some literatures, the performances 1dB compression and IP3 can also present the nonlinearity.
I am confused by that, Is there any relationship between these perforamnces? Anyone can give me a clear idea.

Thanks in advance!

Title: Re: How to simulatue a Gm-C integrator?
Post by Geoffrey_Coram on Mar 3^rd, 2006, 4:14am

tumeda wrote on Mar 3^rd, 2006, 2:18am:

In some literatures, the performances 1dB compression and IP3 can also present the nonlinearity.
I am confused by that, Is there any relationship between these perforamnces? Anyone can give me a clear idea.

One can estimate the 1dB compression point by iIP3 (input IP3) - 9.6 dBm.

The 1dB compression point is the input power at which the output power is 1dB below the ideal "linear" curve followed for low power. The "missing" power is lost through nonlinearities to other harmonics. I guess the assumption is that most of these harmonics are the 3rd order: 2*f1 - f2 and 2*f2-f1. (You put in two "close" tones, f1 and f2, and you get out not only amplified versions of f1 and f2, but also those two harmonics, which are "close" to the original inputs.)

Title: Re: How to simulatue a Gm-C integrator?
Post by tumeda on Mar 3^rd, 2006, 5:53am

Thanks for Geoffrey_Coram's answers! It seems like the harmonics and distortions result in the nonliearity.
but I am still unclear about how to extract the THD or SNR from the Gm-C integrator? and what is the realtionship between the SNR/THD and 1dB compression/IP3 ?

Title: Re: How to simulatue a Gm-C integrator?
Post by Ken Kundert on Mar 3^rd, 2006, 8:19am

To measure THD you apply a pure sine wave of a particular amplitude and measure the harmonic content in the output signal. Since you put a pure sine wave in, any harmonics must result from nonlinearity in the circuit. However, the THD varies with the amplitude of the signal, so you must give you signal level when you give THD.

IP₃ and CP₁ are also measures of distortion, but they are a bit different than THD. Where THD gives the amount of distortion for a particular signal level, CP₁ is a measure of how big the signal can before it causes a particular level of distortion. IP₃ is somewhat similar in this regard to CP₁, but somewhat indirectly.

SNR is the signal to noise ratio. Or more properly, the maximum achievable signal to noise ratio. It requires that you specify what is an exceptable level of distortion, and then amplitude of the signal that causes that level of distortion and the noise floor. So it combines the two imperfections that limit dynamic range, distortion and noise.

-Ken

You can find more on IP₃ and CP₁ in http://www.designers-guide.org/Analysis/intercept-point.pdf.