  Integrating a thermopile with a low power operational amplifier is an
effective and cost-efficient approach to obtain a high performance compact
Terahertz power detector. Here we present the development of such an integrated
detector, including the fundamental building blocks, the final realization and
related characterization. The responsivity and bandwidth of the detector are
measured in a standard THz CW setup consisting of a closed cycle helium
cryostat and a Quantum Cascade Laser (QCL). The predicted results are compared
with measured data, showing a good agreement. Advantages of existing Golay cell
THz detectors in both sensitivity and NEP figure vanish, in practical use, due
to the enormous increment in dynamic range provided by the linear operation of
the thermopile up to 100 mW of incident power while offering a NEP below
1nW/sqrt(Hz) and a -3dB bandwidth of 6,8 Hz.
