What is a Digital Signal Converter?

A signal converter is a device that converts electrical signals into digital signals through the principle of digital electricity, which requires professional chip processing.

Signal converter

The IK standard signal converter is used with various instruments in the industrial automation control system to realize the conversion of standard signals into switching values and replace the output of PLC under certain conditions.

2. Input signal: 4 ~ 20mA Euro or (1 ~ 5V); 8 channels are standard. (Can be increased)

5. Regulate the input signal source arbitrarily to produce dry contact output at any value.

6. Environmental conditions: The temperature is 0 ~ 55 , the temperature is less than 85%, and it is not used in places with corrosive gas.

1. Adjust the potentiometer W to output a dry contact at a certain point (for example: when the input is 4.8mA, to generate an alarm, that is, adjust the potentiometer W to produce a dry contact.

Opening size: 152mm (width) x 76mm (height)

Installation: panel mounting

A / D converter

An analog-to-digital converter is an electronic component that converts analog signals into digital signals. Usually the signal is sampled and held, and then quantized and encoded. These two processes are implemented at the same time as the conversion.

The analog-to-digital conversion usually goes through the steps of sampling, holding, quantizing, and encoding. In the actual circuit, some processes are combined, such as sampling and holding, and quantization and encoding are implemented simultaneously during the conversion process.

D / A converter

A digital-to-analog converter is a device capable of converting a continuous analog signal into a discrete digital signal. The digital quantity processed by the digital system sometimes needs to be converted into an analog quantity for practical use. This conversion is called "digital-to-analog conversion".

DAC is mainly composed of digital register, analog electronic switch, bit weight network, summing operation amplifier and reference voltage source (or constant current source). Use the digital bits stored in the digital register to control the corresponding analog electronic switches, so that the bit with the number of 1 generates a current value proportional to the bit weight on the bit weight network. The values are summed and converted into voltage values.

Single-Ended to Differential Converter with Gain Set by Resistor

Many applications require differential signals to achieve a higher signal-to-noise ratio, improve the ability to suppress common mode noise, and obtain lower second harmonic distortion, such as driving a modem ADC, transmitting signals through twisted pair cables, Adjustment of high-fidelity audio signals, etc. This requires a circuit that can convert single-ended signals into differential signals, namely single-ended-differential converters ^[1] .

For many applications, the low power fully differential precision amplifier built into the AD8476 is sufficient to perform single-ended-to-differential conversion. However, for applications that require higher performance, an OP1177 precision op amp can be cascaded with the AD8476, as shown in the figure. This single-ended-to-differential converter has high input impedance, (maximum) 2nA input offset current, and (maximum) 60V offset voltage and (maximum) 0.7V / ° C voltage offset from the input.

Single-ended-to-differential converter

Figure 1: This single-ended-to-differential converter can be set by adjusting the ratio of RF to RG.

The circuit in Figure 1 is a dual-amplifier feedback structure. The op amp determines the accuracy and noise performance of the circuit, and the differential amplifier plays a single-ended-to-differential conversion function. This feedback structure suppresses the AD8476's errors, including noise, distortion, offset, and drift. It replaces the op amp feedback loop inside the AD8476 with a large open-loop gain of the op amp. In essence, this structure uses the open-loop gain of the op amp for the input, attenuating the error of the AD8476.

The external resistors RF and RG in the figure set the gain of the single-ended-differential amplifier, that is,

Single-ended-to-differential converter

As with any feedback connection, great care must be taken to ensure system stability. The cascade of OP1177 and AD8476 constitutes a combined differential output op amp. Its open-loop gain is the product of the OP1177 open-loop gain and the AD8476 closed-loop gain. Therefore, the closed-loop bandwidth of the AD8476 adds one pole to the open-loop gain of the OP1177. To ensure stability, the bandwidth of the AD8476 should be higher than the unity-gain frequency of OP1177. When the closed-loop gain of the circuit is greater than 2, this requirement can be relaxed because the resistor feedback network can effectively reduce the unit gain frequency of OP1177 by RG / (RG + RF). The bandwidth of the AD8476 is 5MHZ, so the circuit does not operate at any gain There will be stability issues.

When using an op amp whose unity-gain frequency is much larger than the bandwidth of the differential amplifier, a bandwidth limiting capacitor CF can be inserted, as shown in the figure. The capacitor CF and the feedback resistor RF form an integrator, and the bandwidth of the entire capacitor is:

Bandwidth of the entire capacitor

The reason for the bandwidth equation 1/2 factor is that the output of the circuit is fed back in single-ended rather than differential. Therefore, the feedback coefficient and bandwidth of the circuit must be halved.

If this reduced bandwidth is less than the closed-loop bandwidth of the differential amplifier, the circuit is stable. This bandwidth-limiting technique can also open RG, thereby gaining a gain of 2.