It may be realized through a set of Exclusive-OR gates, allowing the use of a simpler, non-priority encoder as shown below in Fig.12. When operated, the flash ADC produces an output that looks something like this:įor this particular application, a regular priority encoder with all its inherent complexity isn’t necessary. The priority encoder generates a binary number based on the highest-order active input, ignoring all other active inputs. V ref is a stable reference voltage provided by a precision voltage regulator as part of the converter circuit, not shown in diagram.Īs the analog input voltage exceeds the reference voltage at each comparator, the comparator outputs will sequentially saturate to a high state. The following example shows a 3-bit flash ADC circuit: The comparator outputs connect to the inputs of a priority encoder circuit, which then produces a binary output.
#TIME WARNER CABLE ANALOG TO DIGITAL CONVERTER SERIES#
It is also known as parallel A/D converter and is formed of a series of comparators, each one comparing the input signal to a unique reference voltage. The current will be the same as that in Rf. Ĭurrent through 2R connected to +5V = 5V/20KΩ = 0.25 mA In the figure shown above, the negative input is at virtual ground, therefore the current through R TH=0. Thus, according to Thevenin’s equivalent resistance, R TH, Let b3 be the most significant bit and thus is connected to the +5V and all the other switchs are connected to the ground. Digital to Analog Converter with R and 2R ResistorsĪ D/A converter with R and 2R resistors is shown in the figure below.Īs in the binary-weighted resistors method, the binary inputs are applied by the switches (b0-b3), and the output is proportional to the binary inputs.īinary inputs can be either in the HIGH (+5V) or LOW (0V) state. This is why R and 2R method is more preferred as it requires only two sets of precision resistance values. If the number of inputs (>4) or combinations (>16) is more, the binary-weighted resistors may not be readily available. The only condition to look out for is that the maximum output voltage should not exceed the saturation levels of the op-amp. Thus, a desired size for a step can be obtained by connecting the appropriate feedback resistor. The value of the feedback resistor R f changes the size of the steps. In practice, due to the variations in the logic HIGH voltage levels, all the steps will not have the same size. The output is a negative going staircase waveform with 15 steps of -0.5V each. The graph with the analog outputs versus possible combinations of inputs is shown below. The output will be maximum if the switches (b0-b3) are closed. This overall current is then converted to its proportional output voltage. The current through R f will be the sum of these currents. Thus, according to the position (ON/OFF) of the switches (bo-b3), the corresponding “binary-weighted” currents will be obtained in the input resistor. Thus, output voltage also doubles and Output voltage = -(1KΩ)×(1mA)= -1V.So current through the resistor will become 5V/5KΩ = 1mA to flow through R f.R/2 will be connected to the positive supply of the +5V.Current through feedback resistor, R f = 0.5mA (Since, Input bias current, I B is negligible).So, current through R = 5V/10KΩ = 0.5mA.It will be connected directly to the +5V. Thus, voltage across R = 5V.The circuit is basically working as a current to voltage converter. Thus, a corresponding 16 outputs of analog will also be present for the binary inputs. We know that, a 4-bit converter will have 2 4 = 16 combinations of output. Thus, the number of binary inputs is four. The circuit diagram represents a 4-digit converter. The op-amp can also be connected in the non-inverting mode. In the circuit, the op-amp is connected in the inverting mode. Digital to Analog Converter using Binary-Weighted ResistorsĪ D/A converter using binary-weighted resistors is shown in the figure below. Therefore, we will begin with DAC circuitry and then move to ADC circuitry. It is much easier to convert a digital signal into an analog signal than it is to do the reverse. Together, they are often used in digital systems to provide complete interface with analog sensors and output devices for control systems such as those used in automotive engine controls:
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