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-member (Toshiba Corporation)The possibility of realizing a low-voltage and low-power audio-band 7-A modulator has been studied. The current-mode circuit technique has been adopted to enable the modulator operate in less than 3V of supply voltage.The modulator uses analog integrators instead of switched-capacitor-type integrators to avoid the use of analog switches, which enables low-voltage operation of the modulator circuit. A newly designed voltage-to-current converter is used to form an analog integrator. The designed circuit was actually fabricated by using CMOS 0.6,u m process and its characteristic was evaluated. The signal-to-noise ratio of 68dB in 20kHz bandwidth for the Ist order modulator construction was measured from the 2.5V supply voltage when the oversampling ratio is 256.However, only 72dB of the signal-to-noise ratio and 65dB of distortion were measured for the 2nd-order modulator construction, although the operation of the oversampling ratio of 48 was successfully confirmed. We concluded that the low-voltage and low-power operation with less than 3V of supply voltage is possible for the audio-band I A modulator, although the signal-to-noise ratio and distortion issues in the 2nd-order configuration are left for future study.

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