  We examine a Bloch Oscillating Transistor pair as a differential stage for
cryogenic low-noise measurements. Using two oppositely biased, nearly symmetric
Bloch Oscillating Transistors, we measured the sum and difference signals in
the current gain and transconductance modes while changing the common mode
signal, either voltage or current. From the common mode rejection ratio we find
values $\sim 20$ dB even under non-optimal conditions. We also characterize the
noise properties and obtain excellent noise performance for measurements having
source impedances in the M$\Omega$ range.
