An ultra low power CMOS pA/V transconductor and its application to wavelet filters

  • Authors:

  • Peterson R. Agostinho;Sandro A. Haddad;Jader A. Lima;Wouter A. Serdijn

  • Affiliations:

  • Electrical Engineering Department, Technological Institute of Aeronautics, Sao Jose dos Campos, Brazil and Electronics Research Laboratory, Faculty of Electrical Engineering, Delft University of T ...;Electronics Research Laboratory, Faculty of Electrical Engineering, Delft University of Technology, Delft, The Netherlands and Brazil Semiconductor Technology Center, Freescale Semiconductor, Camp ...;Brazil Semiconductor Technology Center, Freescale Semiconductor, Campinas, Brazil 13069-380;Electronics Research Laboratory, Faculty of Electrical Engineering, Delft University of Technology, Delft, The Netherlands

  • Venue:
  • Analog Integrated Circuits and Signal Processing
  • Year:
  • 2008

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Abstract

Two compact ultra low-power CMOS triode transconductor topologies denoted VLPT-gm and Delta-gm are proposed. In both circuits, input transistors are kept in the triode region to benefit from the lowest gm/ID ratio. This allows achieving a small-signal transconductance gm down to hundreds of pA/V, making such transconductors attractive for the synthesis of gm-C filters with cut-off frequencies in the range of Hz and sub-Hz. The gm value is adjusted by a well defined aspect-ratio (W/L) and drain-source voltage VDS, the latter a replica of the tuning voltage VTUNE imposed as drain-source voltage of input devices. VLPT-gm reaches a minimum gm of 1 nA/V, whereas Delta-gm exhibits a gm as low as 400 pA/V. Input-referred noise spectral density is typically 12.33 μV/Hz1/2 @ 1 Hz and 93.75 μV/Hz1/2 @ 1 Hz for VLPT-gm and Delta-gm, respectively. In addition, setting their gm equal to 1 nA/V and arranging them as first-order lossy integrators, Delta-gm presents higher bandwidth with respect to VLPT-gm. Cut-off frequencies are 1.33 kHz and 24 kHz for VLPT-gm and Delta-gm integrators, respectively. Finally, as an application example, both transconductors were used as building blocks to realize a 6th-order wavelet gm-C filter. For both approaches, THD was kept below 1% for signal swings up to 200 mVpp.The design complies with a 1.5 V supply and a 0.35 μm CMOS process and features an overall power consumption of 51 and 114 nW, respectively for VLPT-gm and Delta-gm filters.