Introduction to the Principle and Application of Monolithic IC Multiplication Circuit

Function of the circuit

In addition to general multiplication, analog multiplication has many other uses, such as balanced modulation and demodulation, synchronous detection, voltage-controlled attenuator, oscillator, etc. This circuit diagram is the basic wiring diagram of the single-chip IC multiplier AD532 from Analog Devices. Because it has been laser trimmed internally, the potentiometer used to adjust the X and Y input bias balance can be removed, and only the output bias needs to be adjusted.

How the Circuit Works

AD532 is a 4-quadrant multiplier with differential input, which can perform the operation of EO = [(X1-X2) * (Y1-Y2)] / 10. The input voltage range of each input terminal is 0 ~ + 10V, and the proportional coefficient of 1/10 is usually used.

The IC is a multiplication unit composed of a "Giber" multiplier circuit, which has a low output impedance and does not require external components. The IC has been laser trimmed when it leaves the factory, so there is no need for troublesome adjustments. In this circuit, only the output offset adjustment V is required.

Electrical characteristics

When used as a multiplication circuit, the frequency band is 1MHZ/-3DB. When the linearity requirement is high, the frequency can reach 100KHZ. When used as a VCA, nonlinear distortion is an important factor. The distortion of the X input and the Y input are different. A VCA output with less distortion can be obtained from the Y input signal.

The frequency at which linearity starts to deteriorate is 20~30KHZ, and the distortion is about 1% at 100KHZ. When processing AC signal multiplication, attention should be paid to leakage, which varies depending on the X input or Y input, and deteriorates sharply from hundreds of kilohertz. The output offset drift is 700UV/CLYO, which is several thousand times larger than that of a general OP amplifier. Therefore, when used as a DC-coupled synchronous detector, a high signal level should be used as much as possible to avoid the method of outputting after amplification.

Adjustment

Because there is only offset adjustment in the circuit, only the AD533 without fine-tuning is explained here. Figure A only has an additional variable resistor, which can be adjusted in the same way as the AD532. In the multiplication circuit, leakage adjustment is very important. Use VR2 to adjust XO to balance the X input and adjust the leakage of the Y input to the minimum. Use VR3 to adjust Y0 to minimize the leakage of the X input.

Adjustment sequence: First, make X=Y=0, and adjust ZE to make the output 0. The signal frequency is the actual frequency used. Input a signal with an amplitude of 20VP-P from Y, adjust X to minimize the signal output, and then input the signal from the X input terminal, make Y=0, and adjust YO to minimize the signal output. In the above adjustment, the output bias may sometimes change, and in this case, it must be readjusted. Regarding the adjustment of the proportional coefficient, input a DC voltage of positive and negative 10V at the X input terminal, input an AC signal of 20VP-P from Y, and then adjust RV1 until the output and input voltages are the same.