The system consists of three parts: differential signal source module, triode differential amplifier circuit, and measurement display module. The differential signal source module whose main control is the STC15F2K60S2 microcontroller generates a single-channel adjustable sine wave through the AD chip PCF8591, and generates a dual-channel differential signal after voltage division. The differential signal passes through the transistor differential amplification circuit, and the amplified differential signal is output in two ways. The main control of the measurement display module is STC15F2K60S2 microcontroller, which is connected to an external LCD screen and is responsible for displaying part of the amplitude-frequency characteristics of the circuit.
1. Plan demonstration
The main branch option of this proposition lies in the generation of a single sine wave in a differential signal.
a) Solution 1 uses a bridge RC sine wave oscillation circuit. This circuit can achieve preliminary amplitude and frequency adjustment through two to three sliding rheostats, but it cannot meet the step requirements and will be distorted after each frequency adjustment, so it is discarded.
Figure 1.1 Amplitude-frequency adjustable bridge RC sine wave oscillator circuit design
a) Option 2 uses the PCF8591 chip DA to output a sinusoidal waveform. The advantage is that the frequency amplitude is controllable.
b) Option 3 uses the DDS chip AD9854 to generate a single sine wave.
For the sake of balance between controllability and economy, the second option was finally drawn up, which is to use the PCF8591 chip DA to output a sine waveform.
2. Theoretical analysis and calculation
Input differential mode signal: uid=Ui1-Ui2=2Ui1
Output differential mode signal: uod=Uo1-Uo2=2Uo1
Figure 2.1 Transistor differential amplifier circuit
3. Test plan and test results
The signal source outputs a sine wave of 12.4Hz.
Amplification factor at 1kHz : Avd=uod/uid=27
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