This paper presents the trade-off between surface, biasing current and performance of an analog turbo decoder. It is shown that the biasing current and the parasitic emitter resistor can deteriorate the performance of a decoder. The parasitic emitter resistor depends on the emitter area and the biasing current depends on the maximum decoding speed required. Simulations show that the parasitic emitter resistor can deteriorate the performance by 0.35dB for BER of 10E-2 for a 0.25-µm process from NXP. It is also shown that an increase of seven percent of the size of the transistor can divide the emitter resistor by four and thus reduces the deterioration of performance to 0.05dB. In the same way, reducing the biasing current improves the performance but reduces the maximum decoding speed.