A 1mW 40-190MHz BJT logarithmic biquad

This paper reports measured results from a class-A silicon bipolar lowpass logarithmic biquad. The fabricated chip aims: (i) at low power consumption; and (ii) at the investigation of the functionality - i.e. tuneability and linearity for strong input signals - of the log-domain technique when biasing currents internal to the topology operating points differ considerably. The measured results shown here verify that the technique preserves the desirable features of tuneability and good linearity under such conditions. The circuit was laid out in the P71 LM Ericsson process. With the power consumption ranging from 0.8 to 3 mW a bandwidth of 40 to 190 MHz was achieved. The second order distortion was -37 dB for an input modulation index of 65%. The intermodulation product levels were 30dB below the fundamentals for an output modulation index in excess of 80%.