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Qb 188 amplifier circuit

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Q-bit QB-188 RF Microwave Amplifier .5-100 MHz +15db TESTED


Kind code of ref document : A1. Ref country code : KR. Ref country code : DE. Ref legal event code : Ref country code : CA. This application is a continuation-in-part of and claims priority of U.

The present invention generally relates to an apparatus and a method for improving the switching speed of a transistor, and more specifically, to the use of clamping circuitry to prevent a transistor in a large signal drive stage of an audio amplifier from reaching a saturation voltage. A significant limitation on the performance of a high speed electronic circuit is the relatively long "on-to-off time delay that occurs when the voltage drop across a transistor reaches an intrinsic saturation voltage.

Also, a saturated transistor tends to behave in a non-linear fashion, i. However, there are several measures in the prior art that have been taken to circumvent the problems caused by transistor saturation. One prior art solution to this problem is to insure that the potential across a transistor never reaches a saturation voltage.

For example, a "Baker Clamp" can be employed to prevent a transistor from reaching its saturation voltage by coupling a. This technique was originally developed to improve the switching speed for digital circuits, but has also found use in high speed analog circuit designs. The basic concept of the Baker Clamp is to shunt current away from the base when the collector is nearing saturation, so that the forward voltage drop across the transistor will always be less than the voltage drop across the collector-base junction.

A cathode of a diode 12 is coupled to a collector of an NPN transistor 16, which forms an output node An input node 19 is coupled to an anode of diode 12 and an anode of a diode The cathode of diode 14 is connected to a base of transistor An emitter of transistor 16 is connected to a common ground The base-emitter voltage drop V be is about 0.

When transistor 16 is conducting, the voltage at output node 18 will try to drop to the characteristic saturation voltage of the transistor.

Typically, this saturation voltage is a function of the current and the design of the device and is usually less then 0. If the voltage at the collector drops below the voltage applied to the base, the collector-to-base region of transistor 16 will no longer be reverse biased, which is a condition necessary for proper operation of the transistor. However, since the voltage drop across diodes 12 and 14 is essentially the same, and the base voltage is clamped at the value of two forward biased diode voltage drops, the voltage drop across diode 12 insures that the collector voltage will never drop below the base voltage.

Additionally, the current supplied to diodes 12 and 14 is provided by the same input signal. As transistor 16 approaches a saturation voltage, diode 12 will start conducting, which will provide a shunt through the collector for the input signal current. Therefore, a current feedback loop that supplies the correct amount of input signal current to the base of transistor 16 is provided by the Baker Clamp to maintain a constant on-state voltage, while preventing the transistor from saturating.

The output voltage level is at V out from time zero until time t 0 , which lasts until a time t,. The voltage level across the base- emitter for the inverse step waveform 40 is greater than a saturation voltage 42, as shown in the Figure. A conventional Baker Clamp introduces a slight delay in the on-to-off transition times.

An input 48 is coupled to an anode of a diode 52, and anode of a diode 54, and a cathode of a diode A cathode of diode 54 and an anode of diode 56 are coupled to a base of an NPN transistor A cathode of diode 52 is coupled to a collector of transistor 57 and to an output An emitter of transistor 57 is connected to a common ground Diode 54 and diode 56 provide bi-directional current flow into and out of the base of transistor A turn-on voltage for transistor 57 is provided by a positive signal at input 48, and a turn-off voltage is produced by a negative signal.

When the value of the input signal is negative, diode 56 will conduct and provide a path to discharge any internal built-up electrical charge in the capacitance of the base-emitter junction of transistor 57, which was stored during the conduction on state of the transistor. The input voltage is along a y-axis 62 and time is indicated along an x-axis Beginning at a time equal to zero, an input signal is represented by a negative level 66 until a time t 0 , when a rising edge 68 transitions the signal to a positive step waveform Starting at time zero, the signal has a positive level 80 until a time t 0 , when a falling edge 82 transitions the value of the output signal to an inverse step waveform 86 corresponds to the value of the base-emitter voltage V be.

Also, the value of the base-emitter voltage is clearly more positive than a saturation voltage level A graph 90 displays the input voltage signal along a y- axis 92 and time along an x-axis The input signal has a zero voltage level 96 until time t on , when a rising edge 98 transitions the signal to a positive step waveform At time t off , a falling edge returns the value of the input signal to zero voltage level The output voltage signal has a positive level until a time t 0 , when a falling edge transitions to an inverted but positive level step waveform that has a magnitude equal to the base-emitter voltage V be of transistor Moving from time t ofT , the value of the output signal, increases slightly along a slope that continues until the end of a storage time period t s.

Next, the value of the output signal ramps up along a slope over a time t f , at which the signal is again at level A graph plots the input voltage along a y-axis and time along an x-axis , until at time t on , a rising edge transitions the value of the signal to a positive step waveform Next, at time t off , a falling edge transitions the input signal back to negative level From a time equal to zero, the value of the output signal is at a positive level , until a time t on , when a falling edge transitions the signal to an inverse step waveform , which has a value equal to the base-emitter voltage V be of transistor At a time t off , the value of the output signal rises slightly along a slope for a storage time period t s.

At the end of the storage time, the output signal rises rapidly along a ramp until a time t f , when the signal is again at positive level It is important to note that the output signal closely follows the transitions of the input signal when moving from an off state to an on state. During the first time period or delay t s , the built-up electrical charge in the base emitter junction is being discharged by transistor Once most of the stored electrical charge has drained away, transistor 16 begins the transition ramp from a conductive on to a non-conductive off state.

The time period or delay for this on to off ramp is known in the art as the fall time t f of a transistor. By contrast, in FIGURE 3B, the comparison of graph and graph for the input and output signals, respectively, shows that the use of a negative reverse bias turn-off input voltage and the disposition of diode 56 between the base and input 48 considerably shorten the amount of time for both the storage and fall times for transistor A reduction in both the storage and fall time periods has determine the maximum operating frequency of the circuit.

In large signal audio amplifiers, reliability and sonic performance is negatively impacted by relatively long storage and fall times. FIGURE 4 shows a graph that plots the relationship between the output voltage V ce of a transistor shown along a y-axis as a function of base input current show along an x-axis As the input current to the base increases, the output voltage falls to a uniform voltage that is then independent of the input current - for a clamped signal For a non-clamped signal , the output voltage continues to fall until it reaches a potential below that of the transistor's base.

FIGURE 5 displays the storage time of a transistor along a y-axis as a function of input base current along an x-axis AS the input current to the base increases, the storage time increases linearly for a clamped signal , but increases almost exponentially for a non-clamped signal FIGURE 6 shows the fall time of a transistor along a y-axis as function of input base current along an x-axis As the input current to the base increases, the fall time remains almost constant for a clamped signal , but increase almost exponentially for a non-clamped signal Therefore, it is quite evident from FIGURES 4, 5, and 6 that clamping the voltage across a transistor so that the saturation voltage does not occur decreases the time for the transistor to switch from the conductive on to the non-conductive off state.

In large signal audio amplifiers, any time delays incurred by internal transistor stages switching from on-to-off are exacerbated by the use of negative feedback. In FIGURE 7, three different cases showing the output signals of large signal audio amplifier as a function of time are illustrated. Graph shows an output voltage signal comprising an undipped high frequency sine wave Output voltage is indicated along a y-axis and time and phase are indicated along an x-axis Graph illustrates the effect of applying a Baker Clamp to the circuitry of the amplifier.

Output voltage is indicated along a y-axis and time along an x-axis A sine wave output voltage signal displays "clean" clipping of the positive and negative peaks of the signal, which are "flat topped" because the output signal of the amplifier cannot track the full amplitude of the signal being input.

An amplifier's output voltage swing is always limited by the rails of the amplifier's power supply. A graph illustrates the clipping that occurs when an output voltage signal clamp is not used in the circuitry of an amplifier.

The output voltage is indicated along a y-axis and time and phase are indicated along an x-axis An asymmetric clipped sine wave is shown in graph After a finite storage delay time t 2 there is an abrupt transition or notch in the negative direction for the positive-going half of the sine wave. The converse is also true for the negative portion of the waveform. This phenomena is commonly referred to as "sticking. When output stage transistors enter the region of common mode conduction catastrophic destruction of the devices can occur.

Additionally, a non- linear clipped signal causes the amplifier to produce an intermodulation spectra that is very audible and undesirable when heard on a loudspeaker. In the prior art, Baker Clamps are often employed in the manner illustrated in.

In this Figure, an electronic circuit is shown that uses a typical implementation of a Baker Clamp in a large signal drive stage of a power amplifier.

In particular, diodes and are used as the Baker Clamp for the negative output. These Baker Clamps operate in substantially the same manner as discussed for circuit 10 above. From the foregoing, it will be apparent that a clamping circuit for use with large signal amplifiers is required that does not introduce unacceptable delay, i. The simple prior art Baker Clamp does not meet this requirement.

According to one aspect of the present invention, an open-loop clamping circuit prevents saturation of a transistor in an audio amplifier.

It is desirable to prevent saturation of such transistors due, in part, to the increased turn off time of a saturated transistor. The clamping circuit is coupled between a signal terminal of the transistor and a first voltage source, and operates in a first mode during small signal swings on the first signal terminal to isolate the first signal terminal from the first voltage source.

During large signal swings on the first signal terminal, the clamping circuit presents a low impedance between the first signal terminal, limiting the voltage on the first signal terminal to a predetermined value to prevent saturation of the transistor.

The clamping circuit enables the transistor to turn off in a reduced time relative to transistors that use negative current feedback to prevent saturation, and may be utilized in a variety of audio amplifier configurations and with different transistor types. According to another aspect of the present invention, the total harmonic distortion THD of the audio amplifier introduced by the clamping circuit may be shifted beyond the audible frequency range of human hearing, effectively eliminating the deleterious effects of such THD.

According to further aspects of the invention, audio amplifiers including level shifting, error detection, and multiple inputs for the large signal drive stages are provided.

The objects and features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages, may best be understood by reference to the following description, taken in connection with the accompanying drawings, in which:.

FIGURE 4 is a graph of output voltage versus input current for a clamped and an undamped output voltage signal;.

FIGURE 5 is a graph of storage time versus input current for a clamped and an undamped output voltage signal;.


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Kind code of ref document : A1. Ref country code : KR. Ref country code : DE. Ref legal event code : Ref country code : CA. This application is a continuation-in-part of and claims priority of U. The present invention generally relates to an apparatus and a method for improving the switching speed of a transistor, and more specifically, to the use of clamping circuitry to prevent a transistor in a large signal drive stage of an audio amplifier from reaching a saturation voltage. A significant limitation on the performance of a high speed electronic circuit is the relatively long "on-to-off time delay that occurs when the voltage drop across a transistor reaches an intrinsic saturation voltage. Also, a saturated transistor tends to behave in a non-linear fashion, i. However, there are several measures in the prior art that have been taken to circumvent the problems caused by transistor saturation.

US3676659A - Demodulator for angularly related signals - Google Patents

qb 188 amplifier circuit

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Hitachi HM62256LP-10 HM62256 62256 32K x 8 BIT CMOS SRAM PDIP28 x 2pcs


Nad vs naim Some notes they made. NAD M10 vs. The power output is the same at 8 ohms or 4 ohms, and this is part of the reason they can pack so much power into an integrated chassis: by controlling the maximum output so that With the Nait 5, Naim has broken free of an aesthetic look that served it well for nearly two decades and come up with something entirely fresh and modern looking that deserves top marks. I will be trying a "Teddycap" that will replace all the Naim power supplies here in the near future. Imaging was more precise with the C with Dirac active than with the Naim.

Amplifiers

This family includes models available in 15, 35, 60, 90 and W. This amplifier family is suitable for wireless test applications and EMC testing for automotive requirements, and also the new IEC standard. Shielded aluminum housings are surface-mountable, and can be optionally hermetically sealed for use in stringent environments. The products are offered with optional RoHS compliance, lead Pb -free and tin-mitigated designs. Ideally suited for use as local oscillators in UAV, re-entry vehicle sounding rockets and military ballistics applications. The LT series exhibits negligible microphonics under shock. EM Research Inc. Reno, NV www.

A low noise amplifier (LNA) is necessary to amplify a signal without increasing The QB-LNA was simulated by using Schematic Simulation Advanced System.

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Dt Sheet. This application note highlights data conversion, interface and signal conditioning circuits from issue VI:1 February through issue VIII:4 November Like its predecessor, AN67, this Application Note includes circuits for high speed video, interface and hot swap circuits, active RC and switched capacitor filter circuitry and a variety of data conversion and instrumentation circuits.

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