This circuit is designed for low-frequency, small-drift polarity conversion and same-frequency detection. It operates at frequencies below tens of kilohertz and ensures excellent DC stability by using a double-balanced differential configuration, making it suitable for the entire low-frequency range. The analog switch in this design uses a standard N-channel J-FET. To improve response time, a 12 dB/OCT low-pass filter is added to the smoothing circuit. The detection process employs full-wave rectification, which effectively suppresses higher harmonics. This circuit is commonly used in lock-in amplifiers for measuring small voltages with high precision. The working principle of the circuit relies on an operational amplifier (A1) acting as an impedance buffer. If the front-end stage has a low output impedance, A1 can be omitted. A2 serves as a switching amplifier that alternates between inverting and non-inverting modes. When TT2 is turned on, the non-inverting input is grounded, and the gain becomes -1 (R3/R2 = -1). When TT2 is off, the input signal passes through R4 to A2. Due to the high input resistance, the inverting input follows the non-inverting one, effectively making TT2 act as a voltage follower with a gain of 1. The analog switch composed of TT2 requires the gate-source voltage VGS to swing into the negative direction, reaching the pinch-off voltage VP. To drive the circuit with TTL levels, +5V and 0V are replaced with -VCC and +5V. Alternatively, a CMOS analog switch can be used, but cost considerations must be taken into account. TT1 is a PNP transistor with its emitter connected to -VCC. When the input TTL level is low ("L"), TT1 turns on, allowing current to flow through the collector to +5V, turning off D1, and enabling TT2 to conduct. Capacitors C1 and C2 are included to reduce voltage spikes. When the reference waveform is in phase with the input signal, A2 outputs a full-wave rectified positive signal. If the signals are out of phase by 90 degrees, the output becomes a sine wave. At 90° and 270°, the polarity is reversed, forming symmetrical S-shaped waves. With proper filtering, the output becomes zero regardless of the input amplitude. If the peak input voltage is E1, the average value of full-wave rectification is 2E1/π ≈ 0.636E1. By applying a filter gain of 1.56, the output can provide a DC voltage close to E1. The low-pass filter is designed with consistent parameters, and its cutoff frequency is determined based on the system's response. The cutoff frequency is set to 10 Hz, with a roll-off rate of 12 dB/octave. Component selection is crucial for accurate in-phase and reverse-phase conversion. R2 and R3 must be matched precisely. The on-resistance of TT2 should ideally be zero, but in practice, it is several ohms. To minimize RON, R4 or parallel resistors can be increased. For simplification, the level-switching circuit can use a cut-off N-channel MOSFET or a CMOS analog switch instead of multiple components. This reduces complexity while maintaining performance. Anti-rat ant Solar Cable is a kind of cable specially used for photovoltaic power generation system, its main function is to prevent small animals such as mice and ants from destroying the photovoltaic line. Anti-Mouse Ants Solar Cable,Adapter Cable,Ant Rat Resistant Solar Cable,Ant Resistant Dc Cable Suzhou Yonghao Cable Co.,Ltd. , https://www.yonghaocable.com
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August 31, 2025