Improved thermoplastic polymer blend compositions comprising an isotactic polypropylene component and an alpha-olefin and propylene copolymer component, said copolymer comprising crystallizable alpha-olefin sequences. Impedance levels are examined to determine an impedance ramp andor slope rate, which indicates the rate at which a target tissue is undergoing a phase or state change. Circuitry for power up sequencing an amplifier for an active bias control circuit for the amplifier is also disclosed.