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1.2 Functional Diagram
The functional block diagram of the SE1201 DSP Lock-In Amplifier is shown in Fig.4. On the whole, the SE1201
includes signal conditioners, reference signal generators, an algorithm module and a system control module and so on.
Fig.4 Functional Block Diagram of SE1201
1.3 Reference Channel
The reference channel is used to provide control signal which is associated with the detected signal. The SE1201 reference
input can trigger on an analog signal such as a sine wave or a TTL logic signal. The input is AC coupled and the input
impedance is 1M
Ω
.
Generally, both the sine wave and the TTL signal can be used as the reference signal. However, the generator's sine output
has a small and varying amplitude. Meanwhile, many function generators provide a stable TTL SYNC output which can
be used as the reference. Therefore, for frequencies below 1Hz, a TTL reference signal is required.
The SE1201 lock-in amplifier has two reference signal modes: internal reference mode and external reference mode.
In internal reference mode, the internal oscillator generates a digitally synthesized sine wave which is used to multiply
with the input signal. The phase-locked-loop (PLL) is not used since the lock-in reference provides the excitation. The
phase noise will not affect the internal reference signal. The phase noise is extremely low. This mode can work normally
from 50mHz to 120kHz.
