  This paper presents an analytical model to quantify the measured noise in a
cryogenic bolometer readout circuit. The model includes the contributions from
the bias resistors and sensor resistors, voltage and current noise of
amplifier, and cable capacitance. The model parameters are empirically
estimated using frequency domain analysis of the measured noise data of
indigenously developed Neutron Transmutation Doped (NTD) Ge sensors. The model
is shown to describe noise data for NTD Ge sensors over a wide range of
resistances corresponding to temperatures in the range 20 - 70 mK. Relative
contributions of different components are discussed and it is shown that the
contribution to the overall noise from the differential amplifier at 300 K is
the dominant source. It is observed that the amplifier flicker noise is
significantly lower than that specified in the amplifier datasheet. The present
study also indicates that a desirable value of resistance of NTD sensor
(R$_{NTD}$) from noise considerations is $\leq$ 1 G$\Omega$ at $sim$ 20 mK.
