Sigma Delta based biomedical acquisition systems are popular amongst the possible hardware architectures developed for this purpose. It allows for the creation of high-resolution low power and cost-effective universal systems, where oversampling is used with the advantage of the associated simplified anti-alias filter design. However, spurious idle tone generation is commonly present, whose location in frequency and amplitude are not predictable. Despite their amplitude being typically low, in some applications it may tamper with the signal processing parameters. In the ECG, EMG and EEG processing, idle tones may degrade frequency energy content. Given the non-stationary nature of biomedical signals, time-frequency analysis is the adequate tool for idle tone detection due to its dual representation which includes time localization. The spectrogram along with other quadratic time-frequency representations (QTFR) are applied for idle tone analysis where QTFR’s show to have appealing frequency resolution capabilities under low cross terms amplitude conditions.