Recovering small signals in the presence of noise is the application most suited to the synchronous modulator and demodulator technique. If a DC voltage or low-frequency AC signal is modulated by a higher frequency carrier (also known as “reference”) the input signal is converted to an AC signal – the carrier frequency sidebands. Demodulating the signal uses a similar technique (also known as “phase sensitive detector”) resulting in the recovered sidebands. A low- pass filter is used to remove carrier artifacts and out-of-band noise. Random noise generated in the amplifier integrates to zero if a very long integration time (a very low freq LPF) is used. It is entirely practical to recover a small signal buried in 40dB of random (white) noise with a synchronous detector. This is sometimes also called a lock -in amplifier”.
The sync modulation/demodulation switches SW1 & SW2 are usually good analog switches. To prevent DC offset, it is important to maintain a precise 50% duty
cycle in the reference generator and switches. (Created by Neil P. Albaugh, TI – Tucson)
Online Simulation of the Synchronous Modulator and Demodulator Circuit
The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.
Click the link below to invoke TINACloud and analyze the circuit.
You can send this link to any TINACloud customers and they can immediatelly load it by a single click and then run using TINACloud.