Oscilloscope signal waveform synthesis

1.1 Square wave generating circuit

The 555 timer forms a multivibrator circuit . The circuit amplitude and duty cycle are adjustable, the square wave generated is unipolar, and the rising edge of the waveform is steep.

1.2 Frequency division circuit

The frequency division circuit is composed of a hexadecimal counter 74LS163 and a trigger HEF4013. The counter divides the frequency by an odd number of times, and the trigger divides the frequency by two. The circuit duty cycle is 50%.

1.3 Filter circuit

The second-order active bandpass filter circuit is composed of the operational amplifier TL072 and the passive component RC. This circuit can not only filter out DC and high-order harmonic components, but also amplify the voltage

1.4 Phase shift circuit

As shown in Figure 1, the RC equal amplitude phase shift circuit has an adjustable phase range of 0 to 90 degrees and a constant amplitude.

Figure -1

1.5 Addition Circuit

In-phase summing circuit. It can realize the addition of multiple signals, but the stability is not high

1.6 Peak-to-peak detection circuit

The peak-to-peak value detection circuit is composed of field effect tubes and capacitors. The circuit performance is stable and the detection accuracy is good, but the detection accuracy is average in the high frequency range.

2. Parameter Analysis and Calculation

2.1 Square wave generating circuit frequency and duty cycle calculation

The multivibrator composed of 555 timer is shown in Figure 2. This circuit obtains a periodic rectangular wave by charging and discharging capacitor C. According to the oscillation frequency formula and duty cycle formula , if the square wave frequency is to be 300kHZ, it should be satisfied , and at the same time, the sliding rheostat should be adjusted to make the upper and lower resistances equal, so as to obtain a square wave with a duty cycle of 50%.

Figure -2

2.2 Calculation of frequency division circuit parameters

The frequency division circuit is shown in Figure 3. The square wave obtained by the multivibrator is divided by 15, 5, and 3 through the frequency divider, and then divided by 2 through the D flip-flop, so as to obtain 10kHZ, 30kHZ, and 50kHZ square waves with a duty cycle of 50%, which are used for post-stage filtering.

Figure -3

2.3 Calculation of filter circuit parameters

The filter circuit is shown in Figure 4. The filter is a second-order bandpass filter. The high-pass part is used to filter out the DC component, and the low-pass part is used to filter out the sine waves of 10kHZ, 30kHZ, and 50kHZ. According to the cut-off frequency formula , the resistance and capacitance parameters when the cut-off frequencies are 12kHZ, 32kHZ, and 53kHZ are calculated respectively. To prevent the circuit from oscillating, the amplification factor is taken as less than 1.5 times.

Figure -4[page]

2.4 Phase shift circuit parameter calculation

The phase shift circuit is shown in Figure 1-4-2. The differential input of the amplifier is used to generate a +90-degree phase shift at . If the frequency that generates a 90-degree phase shift is taken as the center, when the frequency deviates, its phase angle is: . In order to obtain an arbitrary phase angle, select an appropriate capacitor value of 0.01u, because the phase adjustment can be achieved by adjusting the 5K sliding rheostat.

2.5 Addition circuit parameter calculation

According to the Fourier expansion of the square wave The Fourier expansion of the triangle wave , the amplitudes and phases of the three sine waves are adjusted to match the formula, and the desired waveform is obtained after adding them together.

2.6 Peak-to-peak detection circuit parameter calculation

The peak-to-peak detection circuit is shown in Figure 5. It uses two TL072 comparators and followers, capacitor charging and discharging, and field effect transistors to maintain peak values ​​to achieve peak detection function.

Figure -5