1. NTU EE LAB 3531 Sampling Methods and Analog Filtering zThe sampling process is of critical importance in radio receivers using digitization at the RF or IF. zCommon sampling techniques using a uniform spacing: yNyquist Sampling yOversampling yQuadrature Sampling yBandpass Sampling

2. NTU EE LAB 3532 Nyquist Sampling zDef: A sampling rate of two times the highest frequency component of the analog signal zSampling a bandlimited signal at Nyquist rate==>Anti- Aliasing

3. NTU EE LAB 3533 Bandlimited Signal in a Practical Sense?? zSolution:The relative amplitude of the undesired signals to the desired signal is important. zQuestion:What is the relative amplitude of the signals occurring above one-half of the sampling rate? zSolution:Undesired signals appearing in the Nyquist band due to spectrum overlap must be lower in power than the largest spurious response of the ADC due to nonlinearity.

4. NTU EE LAB 3534 Bandlimited Signal in a Practical Sense??(Cont.) zTo “relax” this requirement yQ:How much distortion of the desired signal is tolerable? yA:Considering Communication System x1.source information:voice, data, video, etc) x2.desired signal bandwidth x3.undesired signal characteristics(BW, power, signal type)

5. NTU EE LAB 3535 Realizable Anti-Aliasing Filters zMore complicated filters are required to reduce the distortion in the sampled signal due to spectrum overlap for a given sampling rate. z==>High Order z==>Phase response tends to become more nonlinear.

6. NTU EE LAB 3536 Oversampling zDefinition: ySampling at rates greater than the Nyquist sampling rate is called oversampling. z When sampling at a higher rate, a simpler anti-aliasing filter with less stop band attenuation can be used. z Increasingly faster ADCs are required to digitize low frequency signals.

7. NTU EE LAB 3537 Quadrature Sampling zIn quadrature sampling the signal to be digitized is split into two signals. zOne is in phase component; the other is quadrature phase component. z Be sampled at one-half the sampling rate required for the original signal. z At expense of using two phase-locked ADCs instead of one.

8. NTU EE LAB 3538 Bandpass Sampling zFor a bandpass signal, the sampling rate be at least two times the BW( ) of the signal. zThe sampling frequency must satisfied zBandpass sampling holds promise for radio receivers that digitize directly at the RF or IF, since the desired input signals to radio receivers are normally bandpass signals.

9. NTU EE LAB 3539 Effects of Quantization Noise, Distortion, and Receiver Noise zRelationship among quantization noise, harmonic distortion, and receiver noise (thermal noise) zQuantization: yUniform quantization yNonuniform:A-law, u-law, adaptive, and differential quantization

10. NTU EE LAB 35310 Uniform Quantization zStatistically, the error signal is assumed to be uniformly distributed within a quantization level. zMean Squared Quantization Noise Power:

11. NTU EE LAB 35311 Noise and Solution zDithering==>Harmonic Distortion, Thermal Noise(Flat Noise) yBoost Amp Gain zMatching the Input Impedence between the ADC and Receiver Output(50-ohm)==> Quantization Noise yTo place a 50-ohm resistive load at the input of the ADC

12. NTU EE LAB 35312 Noise and Solution zThe Receiver Noise zHigher Resolution==>Smaller Quantization Noise Power==>Less Gain

13. NTU EE LAB 35313 Signal-to-Noise Ratio zTheoretical S/N ratio due to quantization noise:

14. NTU EE LAB 35314 Signal-to-Noise Ratio zTheoretical S/N ratio due to aperture jitter noise: zSources: yExternally by jitter in the sampling clock yInternally by sampling switches zSNR=SNRq+SNRaj

15. NTU EE LAB 35315 Residual Error zDefinition: yResidual error is the combination of quantization noise, random noise, and nonlinear distortion. zMeasure: yOutput signal - input signal(sin wave)

16. NTU EE LAB 35316 Spurious Free Dynamic Range zDefinition: yRatio of the sinusoidal signal power to the peak power of the largest spurious signal in the ADC output spectrum. zApplication: yDesired signal BW less than Nyquist BW zSRDR>>SNR

17. NTU EE LAB 35317 Noise Power Ratio zDefinition: yPSD of noise outside BW of notch filter/PSD of noise inside BW of notch filter zMeasure: yBy using a noise input signal into the ADC zApplication: yDesired signal spectrum with many channels

18. NTU EE LAB 35318 Summay of ADC Specifications for Radio Receiver Application

19. NTU EE LAB 35319 Critical ADC Specification for Typical Application

20. NTU EE LAB 35320 Examples of current high-speed ADC technology