In this paper, The difference between getting the output spectrum directly using spectrum analyzer and obtaining the spectrum digitally in measuring clock jitter effect on continuous-time ΣΔ modulator is analyzed. It is shown that clock jitter can be seen as input-referred or output-referred, depending on the nature of the measurement tool. Quantization noise and jitter noise are analyzed and compared graphically using a simple approach. The presented analysis is verified with system-level simulation of a 4th order bandpass continuous-time ΣΔ modulator.