Direct type ADC
Linear Integrated Circuit Applications
20201120 01:16:08
Directtype ADC
An analogtodigital converter (ADC) converts an analog signal to a digital signal. The digital signal is represented by a binary code, which is a combination of bits 0 and 1.
The block diagram of an ADC is shown in the following figure 
Observe that in the figure above, an analogtodigital converter (ADC) consists of a single analog input and many binary outputs. Usually the number of binary outputs of the ADC will be a power of two.
There are two types of ADCs: Direct type ADCs and Indirect type ADCs. This chapter deals in detail with type ADCs. Direct.
If the ADC performs the analogtodigital conversion directly using the equivalent internally generated digital (binary) code for comparison with the analog input, then it is called as Directtype ADC .
Here are examples of directtype CAN 
ADC counter type Successive approximation ADC Flash type ADC This section describes these Direct type ADCs in detail.
ADC counter type
An ADC counter type produces a digital output, which is approximately equal to the analog input using the internal counter operation.
The block diagram of an ADC type counter is shown in the following figure 
The ADC counter type mainly consists of 5 blocks: clock signal generator, counter, DAC, Comparator and Control Logic.
The operation of a counter type ADC is as follows 

The control logic resets counter and activates the clock signal generator to send the clock pulses to the uh counter, when it has received the start command signal.

The counter is incremented by one for each clock pulse and its valueeur will be in binary (digital) format. This counter output is applied as an input to the DAC.

DAC converts the received binary (digital) input, which is the output of the counter, into an analog output. The comparator compares this analog value, $ V_ {a} $ with the external analog input value $ V_ {i} $.

The comparator output will be '1 ' as long as 𝑉𝑖 is greater than. The operations mentioned in the two steps above will be continued as long as the control logic receives "1" from the comparator output.

The comparator output will be '0 ' when $ V_ {i} $ is less than or equal to $ V_ {a} $. Thus, the control logic receives "0" from the output of the comparator. Then the control logic turns off the clock signal generator so that it does not send any clock pulses to the counter.

At this moment, the output of the counterwill be displayed as digital output . It is almost equivalent to the corresponding external analog input value $ V_ {i} $.
Successive approximation ADC
A type of successive approximation ADC produces digital output , which is approximately equal to the analog input using the successive approximation technique internally.
The block diagram of a successive approximation ADC is shown in the following figure
Successive approximation ADC mainly consists of 5 blocks  Clock signal generator, successive approximation register (SAR ), DAC, comparator and control logic.
The works of a successive approximation ADC is as follows 

The control logic resets all bits of the SAR and activates the generator clock signal in in order to send the clock pulses to the SAR , when it has received the start command signal.
Binary (digital) data present in SAR will be updated for each clock pulse based on the comparator output. The output of the SAR is applied as an input of the DAC.

The DAC converts the received digital input, which is the output of the SAR, into an analog output signal. The comparator compares this analog value $ V_ {a} $ with the value of external analog input $ V_ {i} $.

The output of a comparator will be '1 ' as long as $ V_ {i} $ is greater than $ V_ {a} $. Likewise, the comparator output will be '0 ', when $ V_ {i} $ is less than or equal to $ V_ {a} $.

The operations mentioned in the above steps will be continued until the digital output is valid.
The digital output will be valid, when it is almost equivalent to the corresponding external analog input value $ V_ {i} $.
Flashtype ADC
A flash type ADC produces an equivalent digital output for a corresponding analog input in no time. Therefore, flashtype ADC is the fastest ADC.
The circuit diagram of a 3bit flash type ADC is shown in the following figure 
The 3bit ADC flash consists of a network
The operation of a 3bit flash type ADC is as follows.
Flash type ADC is used in applications where the conversion speed from analog input to digital data needs to be very high.