Divide-multiply-with-only-one-trim
This relatively simple and inexpensive circuit requires one trimming operation and can multiply or divide with a consistent accuracy of greater than 1 part in 1,000. An economical CMOS version of the standard 555 timer chip, in conjunction with a low-drift LM11 error amplifier, and an affordable analog chopper switch, forms a unique voltage-to-duty-cycle converter to produce the challenging transfer function necessary for accurate conversion. An unknown multiplicand voltage applied to the error op-amp circuit's Y input controls the duty cycle of the timer through its pin 5 modulation input. The network between the sink-and-source output of the timer, pin 3, and the state trigger inputs, pins 2 and 6, causes the timer to oscillate. An error feedback signal from the timer's discharge output, pin 7, represents the duty cycle. Integrating this duty-cycle signal with a voltage reference representing full scale and applying the result to the inverting input of the error amplifier closes the feedback loop and ensures high accuracy. The multiplier feeds into another LM11 op-amp, which acts as an input buffer and scaler. A third LM11 filters and buffers the output. Between the input buffer and the output buffer, the timer's duty-cycle output modulates the analog switches of a CD4066 to achieve the desired multiplier output. To perform division instead of multiplication, the op-amp circuit can be reconfigured using jumpers. The output buffer is not required in the division configuration. To calibrate the circuit, the X and Y inputs should be connected together and a 10 V signal applied. The 10-turn span potentiometer can then be adjusted to achieve a 10 V output for multiplication or 1 V for the division configuration. Additionally, it is important to check for zero output at a zero multiplier input. The circuit is designed for 0-10 V inputs and outputs, with a slight overage capability, although other scalings are possible. Star grounding or a heavy ground bus should be employed to minimize offset problems that are inherent to this design.
This circuit operates as a versatile voltage-to-duty-cycle converter, effectively allowing both multiplication and division of input voltages with high precision. The core of the system is built around a CMOS 555 timer, which is well-known for its reliability and ease of use in timing applications. The LM11 error amplifier serves as a critical component that ensures the accuracy of the output by comparing the duty cycle derived from the timer with a reference voltage.
The configuration utilizes the modulation capability of pin 5 of the timer, which allows for precise control over the duty cycle based on the input voltage applied at the Y input of the error amplifier. The oscillation behavior of the timer is defined by the connections made to pins 2 and 6, which are integral for triggering the timer's output. The feedback mechanism established through pin 7 ensures that the duty cycle remains proportional to the input voltage, thus maintaining the integrity of the conversion process.
Furthermore, the use of the CD4066 analog switches enables the selection of the appropriate signal path based on the desired operation—multiplication or division. The reconfiguration process is straightforward, involving jumper adjustments that modify the circuit's behavior without the need for extensive component changes.
Calibration is a critical step in the setup of this circuit. By connecting the X and Y inputs and applying a known voltage, the user can fine-tune the output using the span potentiometer, ensuring that the system provides accurate results across its operating range. The design accommodates input and output voltages from 0 to 10 V, with provisions for other scaling options, making it adaptable to various applications.
To enhance performance and reliability, careful attention should be given to grounding practices. Implementing star grounding or a robust ground bus can significantly reduce offset voltages that may arise from the circuit's layout, thereby improving overall accuracy and stability in operation.This relatively simple, inexpensive circuit requiring one trimming operation can multiply or divide with a consistentaccuracy of greater than 1 part in 1,000. An inexpensive CMOS version of standard 555 timer chip T, in conjunction with low-drift LMll error amplifier A3, an inexpensive analog chopper switch SW, form a unique voltage-to-duty-cycle converter to produce the difficult transfer function necessary for accurate conversion.
An unknown multiplicand voltage applied to the A3 error op amp circuit"s Y input controls the duty cycle of the timer through its pin 5 modulation input. The network between the sink-and-source output of the timer, pin 3, and the state trigger inputs, pins 2 and 6, cause the timer to oscillate.
An error feedback signal from the timer"s discharge output, pin 7, represents the duty cycle. Integrating this duty-cycle signal with voltage reference REF representing full scale, and applying the result to the inverting input of A3, closes the feedback loop and insures high accuracy. Multiplier X feeds into another LMll op amp, A1, which acts as a input buffer and scaler. A third LMll, A2, filters and buffers the Z output. Between A1 and A2, the timer"s duty-cycle output modulates the analog switches of a CD4066 to achieve the desired multiplier output.
To perform division instead of multiplication, reconfigure the op amp A1 circuit with the use of jumpers. Amplifier A2 isn"t required in the division configuration. To calibrate the circuit, connect the X andY inputs together and apply 10 V. Then adjust the 10-turn span potentiometer to achieve a 10-V output at Z for multiplication, or 1 V for the division configuration.
Also check for zero output at a zero multiplier input. The circuit is scaled for 0 -10 V inputs and outputs with a small overrage capability, but other scalings are possible. Star grounding or a heavy ground bus should be used to reduce offset problems that are unavoidable in this design.
This circuit operates as a versatile voltage-to-duty-cycle converter, effectively allowing both multiplication and division of input voltages with high precision. The core of the system is built around a CMOS 555 timer, which is well-known for its reliability and ease of use in timing applications. The LM11 error amplifier serves as a critical component that ensures the accuracy of the output by comparing the duty cycle derived from the timer with a reference voltage.
The configuration utilizes the modulation capability of pin 5 of the timer, which allows for precise control over the duty cycle based on the input voltage applied at the Y input of the error amplifier. The oscillation behavior of the timer is defined by the connections made to pins 2 and 6, which are integral for triggering the timer's output. The feedback mechanism established through pin 7 ensures that the duty cycle remains proportional to the input voltage, thus maintaining the integrity of the conversion process.
Furthermore, the use of the CD4066 analog switches enables the selection of the appropriate signal path based on the desired operation—multiplication or division. The reconfiguration process is straightforward, involving jumper adjustments that modify the circuit's behavior without the need for extensive component changes.
Calibration is a critical step in the setup of this circuit. By connecting the X and Y inputs and applying a known voltage, the user can fine-tune the output using the span potentiometer, ensuring that the system provides accurate results across its operating range. The design accommodates input and output voltages from 0 to 10 V, with provisions for other scaling options, making it adaptable to various applications.
To enhance performance and reliability, careful attention should be given to grounding practices. Implementing star grounding or a robust ground bus can significantly reduce offset voltages that may arise from the circuit's layout, thereby improving overall accuracy and stability in operation.This relatively simple, inexpensive circuit requiring one trimming operation can multiply or divide with a consistentaccuracy of greater than 1 part in 1,000. An inexpensive CMOS version of standard 555 timer chip T, in conjunction with low-drift LMll error amplifier A3, an inexpensive analog chopper switch SW, form a unique voltage-to-duty-cycle converter to produce the difficult transfer function necessary for accurate conversion.
An unknown multiplicand voltage applied to the A3 error op amp circuit"s Y input controls the duty cycle of the timer through its pin 5 modulation input. The network between the sink-and-source output of the timer, pin 3, and the state trigger inputs, pins 2 and 6, cause the timer to oscillate.
An error feedback signal from the timer"s discharge output, pin 7, represents the duty cycle. Integrating this duty-cycle signal with voltage reference REF representing full scale, and applying the result to the inverting input of A3, closes the feedback loop and insures high accuracy. Multiplier X feeds into another LMll op amp, A1, which acts as a input buffer and scaler. A third LMll, A2, filters and buffers the Z output. Between A1 and A2, the timer"s duty-cycle output modulates the analog switches of a CD4066 to achieve the desired multiplier output.
To perform division instead of multiplication, reconfigure the op amp A1 circuit with the use of jumpers. Amplifier A2 isn"t required in the division configuration. To calibrate the circuit, connect the X andY inputs together and apply 10 V. Then adjust the 10-turn span potentiometer to achieve a 10-V output at Z for multiplication, or 1 V for the division configuration.
Also check for zero output at a zero multiplier input. The circuit is scaled for 0 -10 V inputs and outputs with a small overrage capability, but other scalings are possible. Star grounding or a heavy ground bus should be used to reduce offset problems that are unavoidable in this design.