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8
The phase difference is defined as:
)
/
(
tan
1
X
Y
.
1.2 Functional Diagram
The functional block diagram of the SE1022D DSP Lock-In Amplifier is shown in Fig.4. On the whole, the SE1022D
includes signal conditioners, reference signal generators, an algorithm module and a system control module and so on.
Fig.4 Functional Block Diagram of SE1022D
1.3 Reference Channel
The reference channel is used to provide control signal which is associated with the detected signal. The SE1022D
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. When a TTL signal is used as
reference signal, high voltagelevel is defined when the voltage exceeds 2.5V and low voltagelevel is defined when the
voltage is lower than 0.4V. When a sine wave signal is used as reference signal, the signal is AC coupled, with signal level
greater than 0.4Vpp. Usually a generator’s sine wave output has a small variation in amplitude while many function
generators provide a stable TTL SYNCD output which can be used as the reference. Therefore, when the frequencies