Excessive energy consumption of UHF tag is the bottleneck of energy saving in its wide range of applications. To address this issue, a lower power design for UHF RF CMOS circuits based on power consumption acuity is proposed in this paper. Through in-depth analysis of the static and dynamic power generation principle of UHF RF circuits in the work, the power consumption acuity can be calculated by using the correlation of circuit power and input vector. Subsequently, under the guide of this acuity, the UHF RF CMOS circuits with better energy saving can be designed. Furthermore, according to the performance indicators of EPC CIG2 UHF RFID in UHF identification, the corresponding circuit is designed and implemented. The test results show that the design of UHF RF circuit based on the acuity of power consumption can reduce 35%–40% power consumption.
Compared to other automatic identification technologies, the most prominent feature of RFID is that it is the fast noncontact technology in identification of moving objects and has high accuracy, security, and resistances to harsh environment, which can also identify multiple recognition objects and so on [
The researches of UHF and microwave bands tag chip got a late start, and most of them have focused in 2003–2006. Among them, the paper about tag chip research published in the literature [
The remainder of the paper is organized as follows. Section
Power consumption of CMOS circuit can be divided into static and dynamic power consumption. The static power consumption is caused by the charging and discharging of large parasitic capacitance, which is considered the main source of power consumption in the circuit. The dynamic power consumption is mainly caused by the PH junction leakage current, gate leakage, and subthreshold current of the transistor; it is the important part of the overall power consumption.
Dynamic power consumption is considered to be the main source of power consumption of UHF RF CMOS circuits, which is produced from the handover of tag identification circuit between two stable operating states. It consists of two parts: one is the power consumption of capacitor caused by the charging and discharging of capacitor in RF circuit reverser; the other is the power consumption of moment conduction generated by the instant conduction of tubes
The charging and discharging of the load capacitance from UHF RF inverter.
According to the working principle of UHF RF inverter, when the jump-behavior of the CMOS inverter input end
In the process of UHF RF circuit operation, the average power consumption
In the above formula,
It can be obtained from the principle of charging and discharging of the CMOS inverter:
Therefore, it can be obtained as (
In the above formula,
Thus, the power consumption of instantaneous conduction is
When UHF RF circuit is in a steady state, the leakage current of inverter exists, which is the reason of static power generation. If
It is the solution equation of subthreshold leakage current, while subthreshold leakage current is measured value which cannot be ignored in test circuit simulation of BSIM. BSIM is the industrial standard of test circuit simulation, which is developed by University of California in Berkley and used to test circuit simulation and development of CMOS technology. It is software simulation system based on physics and occupies the characters like preciseness, upgradability, robustness, and language, which can also provide the data of Dc analysis, transient analysis, and Ac analysis of standard circuit. It is the current between source and drain electrode when the circuit is at rest. BSIM model can accurately test the subthreshold leakage current [
In this equation,in the solution process of subthreshold leakage current
With the deepening of the process, the increasing of gate leakage current is much faster than subthreshold leakage current, which can be indicated in formula (
Consider the following:
When the strong electric field is formed between reverse-biased P-N junctions, it will form BTBT (Reverse Biased Band to Band Tunneling) leakage current; it can be represented by using formula (
By the preceding theory, the dynamic power of UHF RF circuit is essentially the valid statistics for jump variables of input signal. In this section, the power acuity analysis is researched in-depth. Acuity of power consumption is the correlation degree of power consumption and input vector. It is a very important character of power consumption. It also can be used in low power design. If the acuity of power consumption is considered enough in the design of UHF RF circuit, it can perform an UHF RF circuit with relatively small power consumption.
The power consumption of UHF RF circuit is generally divided into static and dynamic power consumption. Dynamic power consumption is considered to be the main source of power consumption of UHF RF circuits. It is produced from the switching process of UHF RF circuit between two stable operating states, which consists of two parts: one is the power consumption of capacitor caused by the charging and discharging of capacitor in RF circuit reverser, the other one is the power consumption of moment conduction generated by the instant conduction of
The probability of which signal is set to 1 and signal activity are the important indicator to measure power consumption acuity. It can reflect validly the active character of circuit and reflect the power consumption acuity directly. Assume that the action of UHF RF circuit is the 0-1 process of each state, which is represented by the function
Signal probability can be represented by formula (
By means of analysis, when the random probability of which signal is set to 1 is 1/2, signal activity is 1/2, and the effect of power consumption acuity is the best.
As the same definition, the signal activity of
After defining the signal probability and signal activity, the transmission characters of signal probability and signal activity are further to define.
The transmission characters of the probability which signal is set to 1 are that the signal probability of basic logic gate output signal is represented by a function of the input signal probability. Assume that a two-input gate AND input signal probability is
For
The hopping transfer characteristics of basic logic gates figure.
After the research on the character of signal probability and signal activity, the transmission characteristics of the basic logic gate transition rate are available. On the basis of this, power consumption acuity can be analyzed. In the circuit design process, the method of low-power design is based on the transmission character of jump rate: if the circuit logic gate with a larger probability is near to the control value, then the design of UHF RF circuits will be with the relatively small power consumption.
The power consumption acuity is the correlation degree of power consumption and input vector. It is a very important character of power consumption.
Power consumption acuity is the changing rate of circuit power consumption probability which is set to 1. The definition is as follows:
In this equation,
Consider the following:
In this equation,
Through the previous studies on signal probability and signal activity and their transmission characteristics, a simple calculation method for power consumption acuity based on the transmission characteristics of transition rate can be obtained. Firstly, the signal probability and signal activity of given input vector can be adopted to make statistical analysis, and through the transmission character of signal probability, the signal probability of each circuits gate can be calculated. The signal activity of circuit input signal is set to the signal activity of input vectors, and then by the transmission characteristics of signal activity, the input and output signal activity value of the entire logic gate at the input terminal can be obtained. The sum of signal activity values
In this formula,
By using the acuity analysis of the power consumption, the average dynamic and static power consumption of UHF RF circuit can be calculated.
In the process of UHF RF circuit design, in order to reduce power consumption, it can be considered to reduce the power consumption acuity in low power design. If the logic gate of UHF RF circuit exists with a greater probability at the value in the control, the designed UHF RF circuit will have relatively small power consumption compared to the other. According to this conclusion, minimizing the power consumption acuity can make the circuit relatively stable in the UHF RF circuit design. Definitely, the appropriate transformations of the circuit can also lead to lower power requirement in UHF RF circuit design. The acuity in the respective input terminal of the circuit is difference, and one of the greater acuities can be selected as the control parameter, and the phase deviation of the UHF RF can be suppressed effectively. The power consumption is reduced greatly.
Experiment circumstance: the experiments about acuity analysis of energy consumption are presented; the analysis is achieved by C++; the platform is VC++6.0, at the same time, running on the Precision T7610 ((Inter xeon processor E5-2620 v2 (6 cores HT, 2.1 GHz Turbo, 15 MB) Windows 7 professional 64 bit, 16 GB (4 × 4 GB) 1866 MHz DDR3 ECC RDIMM, 1 TB, 3.5 inch Serial ATA (7,200 Rpm) HDD, 2 GB NVIDIA Quadro K2000 (2DP & 1DVI-I) (2DP-DVI & 1DVI-VGA adapter))) workstation.
To validate the effectiveness and energy efficiency of the proposed design of UHF RF circuit based on the power consumption acuity, according to the performance indicators of EPC CIG2 UHF RFID and the power acuity theory, a UHF RF front-end circuit with the reset terminal which is suitable for the power-sensitive work is presented here. The general structure is shown in Figure
The in front-end rectifier of UHF RF circuit.
Compared with the conventional rectifier, the delay of rectifying portion in the front end of UHF RF is small, and the leakage is low under the same operating voltage. In order to reduce the static and dynamic power consumption of circuit, the increase of circuit drive capability makes the size of the rectifier relatively large; this is not obvious for the small-scale digital circuit. When the circuit is operating in strong inversion region, it can reflect its superiority. Figure
Comparison results of power consumption.
As it is shown in Table
Energy consumption of different triggers.
Temp | 80°C | 66°C | −30°C | ||||||
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Comer |
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|
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|
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|
|
|
|
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|
0.245 |
0.346 |
0.325 |
0.345 |
0.446 |
0.425 |
0.345 |
0.456 |
0.416 |
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|
1.77 |
2.8 |
3.55 |
211.5 |
321.44 |
265.65 |
234.5 |
314.44 |
265.65 |
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|
1.43 |
1.96 |
2.77 |
111.4 |
223.44 |
162.46 |
175.4 |
267.44 |
162.46 |
According to the theory of acuity analysis, in this paper we use the transmission gate structure and increase the width to length ratio of transistor appropriately. The delay of the rectifiers designed in this paper is smaller than the traditional structure for 9.6 us under the same supply voltage and load (the NOT gate in this paper), and the consumption decreases by around 36%.
For a long time statistical analysis, the total loss curve
Comparison of minimum loss.
In accordance with the approximate solution and the exact solution, the optimal voltage curve
Comparison of optimal voltage.
In this paper, we reviewed the design approach or procedures of UHF tags. In response to the problem of high energy consumption, we present a lower power design for UHF RF CMOS circuit based on the power consumption acuity. The simulation results show that
The authors declare that they have no conflict of interests.
This work was supported by Beijing modern agricultural technology system, Poultry innovation Team, 2013 Beijing New Rural Base Constructional Project.