Research Article Volume 4 Issue 6
^{1}Guru Gobind Singh Indraprastha University, India
^{2}Department of electronics and communication engineering, Jamia millia islamia (Central University), India
Correspondence: Pawan Whig, Vivekananda Institute of Professional Studies, Guru Gobind Singh Indraprastha University, New Delhi, India
Received: March 18, 2017  Published: December 3, 2018
Citation: Whig P, Ahmad SN. Comparison analysis of various R2R D/A converter. Int J Biosen Bioelectron. 2018;4(6):275273. DOI: 10.15406/ijbsbe.2018.04.00140
This paper presents the study of R2R D/A converter using various topologies like CMOS, Transmission Gates TG) and OPAMP. For the sake of simplicity 4 bit input is taken. The R2R D/A converter consist of only two values of resistor R & 2R. By using the repetitive arrangement of precision resistor network in a ladder. The simulation of the R2R D/A converter has been done on the TANNEREDA TSPICE and the circuit verification has been done on SEDIT on TANNEREDA software package. Simulation results are included to demonstrate the results. The outcomes of simulation are fairly in agreement with the theoretical estimation.
Keywords: R2R D/A, CMOS, Opamp, transmission gates
Most of the modern wireless communication systems require a wireless frequency (RF) subsystem.^{1} The design of RF system consists of various components ranging from connecting modules to power supply, antenna, baseband layer, and other interfaces, constitute a radio system.^{2‒4} The main front end radio transmitter module consists of digital signal processor which processes the input digital signal to analog output signal and vice versa. In other words, a discreteamplitude; discretetime digital input signal is converted into a continuousamplitude, continuoustime analog counterpart. In most of the cases the input digital signal is a binarycoded representation of an analog signal using N bits. The leftmost bit of the input digital word is usually called the mostsignificant bit (MSB), and the rightmost bit is called the leastsignificant bit (LSB).^{5‒7} Now with the advancements in VLSI technologies CMOS based current mode DACs are the very much for many applications. The main features of CMOS like their high speed, low power, and cost effectiveness enable it successful for the implementations in designing of circuits.^{8‒10} Nevertheless the digital to analog converter (DAC ) can equally be used as a standalone chip for SoCs. There are several digital to analog architectures for DAC designs which includes resistor string, R2R ladder networks, charge scaling, current steering, and segmented current steering.^{11‒13 }Common problem with DAC to avoid glitches because of the rapid change of more than one digital input bit at a sampling time causes noise problems since resistors are noise sources. Because of which DAC output dose not result in expected value.^{14‒17} In this research studies a comparative R2R DAC using various CMOS topologies has been presented. It is well known fact that the binary weighted resistor D/A converted requires a wide range of resistance value and matched switch for each bit position.^{18‒22 }The R2R D/A converter with an R2R ladder network which eliminates these complications at the expense of an additional resistor for each bit is shown in Figure 1. Bit MSB and LSB are driven from logic gates. The operation of this converter can be considering the weights of different bits one at a time. This can be followed by superposition to construct analog output corresponding to any digital input word.
Figure 2 shows the R2R D2A converter using CMOS inverter. CMOS inverter is attached in series with next CMOS inverter for 1 bit and the R2R series is attached with it, and then it gives output the same bit as input. The same process is repeated for all the bits. Figure 3 presents output in the analog form. The output Fig. 3 of the R2 D/A converter is followed by the voltage as the voltage at node (n1) is given by
V _{n1} = V_{R(} $\frac{\text{R}}{3R}$ _{)}
V_{out} =  $\frac{{V}_{R}}{2}$
The weight of MSB is  $\frac{{V}_{R}}{2}$ .
R2R D/A converter using TG
Transmission Gate (TG) is used in digital CMOS circuit design to pass or not pass a signal^{2325 }In other words, It acts like switch. The gate is made up of the parallel connection of p and n channel MOSFET. When S is high then the transmission gate pass the signal on the input to the output. Transmission gate using CMOS and its circuit and symbols are shown in Figure 46. In the Figure 7 R2R D/A converter is using TG. In this b_{0}, b_{1} ,b_{2} and b_{3} is the digital signal . The TG is a good switch and when the digital pulse is given to all the bit it gives the output Figure 8 corresponding to the analog signal.
R2R D/A converter using OP AMP
The Figure 9 shows the internal circuit of opamp which is used in the R2R D/A converter using opamp. When data is in binary form, the 0's and 1's where the logic zero may be a value up to 0.8 volts and the 1 may be a voltage from 3 to 5 volts.^{2628 }The data can be converted to clean digital form using gates which are designed to be on or off depending on the value of the incoming signal. Data in clean binary digital form can be converted to an analog form by using a summing amplifier. For example, a simple 4bit D/A converter can be made with a opamp. where the D's take the value 0 or 1. The digital inputs could be TTL voltages which close the switches on a logical 1 and leave it grounded for a logical 0. This is illustrated for 4 bits, but can be extended to any number with just the resistance values R and 2R. Input summing amplifier. More practical is the R2R Network DAC. In the Figure 10, the negative input is at virtual ground, therefore the current through R_{TH}=0.
Current through 2R connected to +5V
$\frac{5V}{20}$ = kΩ=0.25 mA
The current will be the same as that in Rf.
V_{o}= (20kΩ)*(0.25mA)=5V
Output voltage equation is given below.
${V}_{out}={R}_{f}\left[\frac{{B}_{3}}{2R}+\frac{B2}{4R}+\frac{B1}{8R}+\frac{B0}{16R}\right]$
The output is shown in Figure 11. with respective to the digital input and converting in analog output.
D/A using OPAMP
Inference from Table 1 for the same technology i.e. CMOS technology developed for all the three design styles and the same power supply we arrive at the following comparative results:
Design Style 
CMOS 
TG 
OPAMP 
Properties 



Technology Used 
CMOS 
CMOS 
CMOS 
Power supply(VDD, GND) 
3.5V0V 
3.5V0V 
3.5V0V 
Resistors 
9 
9 
10 
No. of components 
16 MOS 
4 TG (8 MOS) 
6 MOS 
Average Power dissipiation (Watts) 
1.02E02 
3.80E03 
2.94E02 
Maximum Power dissipiation (Watts) 
9.67E03 
4.67E03 
4.13E02 
Table 1 Comaprision ananlysis of various designs
This indicates the area of fabrication with the earlier two is least. The average power dissipation for the above three cases in Watts is listed as:
From this we come down to the conclusion that the average power dissipated is maximum in case of OPAMP based R2R D/A circuit and the minimum in the case of TG. The Maximum power dissipation for the above three cases in Watts is listed as:
From this we come down to the conclusion that the Maximum power dissipated is maximum in case of OPAMP followed by CMOS and TG as indicated above.
In this paper, R2R D/A circuit employing various topologies like CMOS, TG, and OPAMP is proposed. As a result of the various analysis made we arrive at following important results OPAMP > CMOS > TG  The average and maximum power dissipation (in Watts) CMOS > TG > OPAMP (No. of component used).The above results shows that although the implementation of R2R D/A circuit with OPAMP dissipated more power but it requires less number of component as compared with other two topologies. The various advantages of implementing R2R D/A circuit is that it’s very easy principle of working and construction another one its fast conversion rate as compared to other circuits. These advantages responsible for its use in audio and video techniques
None.
Author declares that there is no conflicts of interest.
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