A 1.2-V n-p-n-only integrator for log-domain filtering

A simple log-domain integrator that operates nominally with a supply voltage of 1.2 V is proposed. It does not employ p-n-p or positive metal-oxide-semiconductor (PMOS) transistors in the signal path. This has two advantages: (1) It makes the integrator suitable for high-frequency applications. (2) The circuit can be implemented using low-cost bipolar processes rather than the more expensive bipolar complementary metal-oxide-semiconductor (BiCMOS) processes or the bipolar processes featuring high-quality p-n-p transistors. A third-order Chebyshev prototype filter, employing the proposed integrator, is realized using a semicustom bipolar array. It consumes 282 μA per pole for a cutoff frequency of 1.5 MHz, achieving a 40.5 dB dynamic range. For lower biasing currents, the circuit can operate from a supply voltage as low as 0.9 V. Detailed experimental results are reported and discussed