High efficiency wide bandwidth power amplifier

BACKGROUND OF THE INVENTION

In all previous signal amplifying methods, both for low and high frequencies there are lots of disadvantages and problems such as low efficiency, large circuit size, high costs, limited bandwidth and etc. All mentioned disadvantages make power amplifier designer or communication designer to suffer complexity in design, time consuming procedure and high costs. In fact every method has its own limitations and these limitations prevent a designer not to reach the ideal point (such as high bandwidth, high efficiency, simplicity in design, smaller size . . . ). Amplifiers are categorized in different classes. Current common amplifiers work in A/B/AB/C/D/E/F classes.

SUMMARY OF THE INVENTION

This new idea is discussing, how to increase the efficiency of an amplifier with clipping the signal that is about to be amplified. Clipped signals will be amplified separately and then they will be summed together in order to make the original input signal but with more power. which is called out put signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1-A illustrates a sinewave generator in which a pure sinewave is transferred into the clipping stage; wherein clipping stage clips signal into defined number of clipped signals.

FIG. 1-B illustrates clipper stages' output.

FIGS. 2-A, 2-B illustrate conception of clipping signal into more pieces if needed.

FIG. 3 illustrates a circuit that consisted from symmetric power supply and SW1, SW2 . . . SW8. If the status of switches is changed with special order (in accordance with input signals), the signal at the load terminals is amplified input signal.

FIG. 4 is similar to the FIG. 3, except instead of mechanical switches, BJT transistors were replaced.

FIG. 5 is similar to FIG. 4 except which instead of BJT transistors, MOSFET transistors were replaced.

DETAILED DESCRIPTION OF THE INVENTION

By clipping a signal and amplifying each clipped part then adding each amplified part, we can obtain pure high amplified input signal with high efficiency, high power, lower T.D.H, lower design costs and small size. For amplifying clipped parts both linear and non-linear methods can be used. In this new method, we exploit spontaneous power of transistors.

For simplicity we assume that we are going to amplify a pure sine signal, and output signal is high power amplified input. According to the new method, the main signal should be clipped into number of specific parts. For example we clipped the main signal into 4 equal parts. Like Figures A and B, we amplify each part, and then by adding each amplified clipped signals, we obtain amplified pure sinewave as output. By clipping the signal into more pieces (referring to Figures A and B), for example, clipping every half cycle into four equal parts, we have eight equal parts. Now for amplifying each part, there are two common ways:

- Linear method
- Non-linear method

Each of both methods has their own advantages and disadvantages. Now we explain each method.

Linear Method:

Considering the fact that all transistors in FIG. 3 are linear, the signal at the load terminals are exactly pure sinewave, of course high power amplified one (for better understanding assume every transistor like variable resistors which can range from fraction of an ohm to several hundred mega ohms). The final amplified sinewave is illustrated in FIG. 4 and FIG. 5 (in FIG. 4 transistors are BJT and in FIG. 5 transistors are MOSFET).

Analysis of FIG. 4 and FIG. 5:

Each of Q1, Q2, Q3 and Q4 transistors work in clipped positive half cycle (each of them works in a quarter of positive half cycle).

Each of Q5, Q6, Q7 and Q8 transistors work in clipped negative half cycle (each of them works in a quarter of negative half cycle).

As a result, load's terminals signal, is a summation of 8 amplified signals in which collectively makes high power amplified pure sine wave. Performances of both circuits in linear region in FIG. 4 and FIG. 5 are the same and with approximations, analysis for each of them is similar. Also circuits in FIG. 4 and FIG. 5 can work in both switching region and linear region.

If you are about to amplify clipped signal by switching method, circuit in FIG. 5 has some advantages in contrast with circuit in FIG. 4, because MOSFETs have very small Rds_(on), so if used as a switch, the loss will be decreased considerably versus BJTs. As well as this, MOSFETs don't need high continuous current at the gate, while BJTs using high current at the base.

Transistors Performance Analysis in Switching Region

If transistors that are working in linear mode, work in switching mode, for generating THE sinewave, power source should follow switches and vary similar to our arbitrary wave, or we need to generate SPWM signal, and every SPWM cycle should be clipped and then applied to the switches. Even you can generate square wave with constant duty cycle and then clip and amplify it, after amplifying you simply convert it to sine wave. However in the application that we need sinewave with variant frequencies, the best choice is using SPWM (like amplifying voice).

The efficiency for amplifying clipped signals in the switching mode is higher than linear mode (for better understanding you can imagine that a transistor can be replaced by variant resistor in linear mode, and as a switch in saturated mode).

Each transistor has a short performance in every cycle, so if any problem occurs in a cycle, it can only affect a small part of it not the whole cycle. As well, if transistors heat up during their performance, they will have enough time for cooling in the rest of the cycle. Because of the short performance in each cycle, transistors could be used with permitted spontaneous current which is much higher than permitted continuous current, using transistors in this current, can lower the costs and let us to have cheaper transistors in our designs.

In amplifying, if we use a transistor in the whole cycle or half cycle, it will be heated up and consequently, by increasing the resistance of the conductance the loss will increase. But in this new method, transistors have enough time for cooling and never heat up, so the efficiency in this method is higher. High power and high frequency transistors are very expensive, using this method let us to use low frequency transistors in which they are much cheaper. As well as this, in power electronic, it is possible to manufacture transistors that tolerate much higher spontaneous current, in this case the size of transistors could be much smaller. Because of lower Rds_on, impedance matching is easier, and so it is another advantage for this method. Implementing this method into an integrated circuit is convenient, if this happen, in the future we will witness amplifying integrated circuit with high bandwidth, high power, high efficiency and low costs.

Below equation describes loss equation in each transistor for clipped signal in switching mode amplification.

$\underline{P_{loss}} = \frac{1}{T} \int_{0}^{\frac{t}{n}} Vswitch (sat) \times Iswitch (\max) dt$

In this formula ‘n’ represents number of switches (in fact it represents the number of clips in each signal) and T represents the time.

V_satrepresents switch terminals' voltage when it is fully on.

I_switchshows maximum switch current when it is fully on.

Total Circuit Losses (Whole Transistors' Loss):

$\underline{PdT} = \sum_{m = 1}^{\infty} (Ploss) m$

In the above equation ‘m’ represents the number of switches.

As much as the number of the signal clips increases, efficiency will be improved and T.H.D will be decreased.

Approximate efficiency equation is:

$Efficiency = \frac{Poac (\max)}{Poac (\max) + [\frac{1}{T} \int_{0}^{\frac{1}{n}} Vs (sat) \times Is (\max) dt]}$

The above mentioned equation is for each transistor in which instead of integral equation you can replace below series to obtain overall efficiency:

$Efficiency = \frac{Poac (\max)}{Poac (\max) + [\frac{1}{T} \int_{0}^{\frac{1}{n}} Vs (sat) \times Is (\max) dt]}$

Industrial Applications:

This new method has a very high potential for applying in the industry and in the industrial process. Some of these applications are listed below:

- Coast to sea navigation transmitters
- Sea to sea navigation transmitters
- Land to land navigation transmitters
- Land to space and space to land transmitters
- Broadcasting transmitters
- Audio amplifiers
- Induction heating and more.

In FIG. 4, the performance of the BJT transistors are similar to the mechanical switches but the only difference is that, BJT transistors can work in both linear region and switching region.

In FIG. 5, in some cases using MOSFETs has a better characteristics in contrast with BJT transistors.

In the end, the current invention comprises high efficiency and could reach up to 99%. The method has high Bandwidth. The slope of the bandwidth for this new method is equal to 1. In other words from zero frequency (DC) to cutoff frequency of switches it can amplifies signals in high powers. It has low T.D.H; wherein the total harmonic distortion can reach below 0.1. It has a compact design, in contrast with other previous methods this method has high potential to result in designing high power amplifiers up to several hundred watts, of course, with smaller size and lower costs.

High efficiency wide bandwidth power amplifier

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