Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
1998-12-21
2001-07-03
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S427000
Reexamination Certificate
active
06255885
ABSTRACT:
The present invention relates to low voltage transistor biasing, for example for use in a power amplifier.
DESCRIPTION OF THE RELATED ART
Field effect transistors (FETs) in power amplifiers can be used to control the gain of the amplifier by adjusting the gate-source voltage (V
GS
) of the transistor. In some cases, for example, MESFET transistors, it is necessary to bias the gate of the transistor with a negative voltage. However, since the negative bias voltage has to be generated from a limited common positive supply voltage, like a battery, negative voltages of high magnitude are difficult to generate.
In some applications, for example, in radio telephones, it is necessary to be able to turn the transistor completely off so as to guarantee that very little radio frequency energy is transmitted when the phone is not supposed to transmit.
This can be accomplished by biasing the gate of the transistor to a DC level which ensures that the voltage at the gate never reaches above the turn-on voltage of the transistor.
The DC bias voltage determines how much of the AC signal is amplified, which therefore determines the gain of the amplifier in a large signal situation, such as a power amplifier. Thus, a large negative bias voltage will ensure that the transistor remaining in an off state. For example, for an input AC signal of ±1.5 V, and the turn-on voltage of the transistor being −1.5 V, the DC bias voltage would need to be −3 V or lower.
To achieve a DC bias voltage of −3 V from a common supply voltage of +3 V, previously used amplifiers have used a DC/DC converter. The most simple DC/DC converters (charge pumps) include a capacitor and a switch to produce a negative voltage. The switch gives some loss and a reasonable converted negative supply voltage which can be expected is thus −2.5 V. One way to improve this is to add another capacitor which is fed by the generated negative supply as ground, which gives a reasonable negative supply of −5 V. However, the extra components add cost, consume space, and are hard to integrate, since the capacitors have to be fairly large.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided a field effect transistor circuit comprising a field effect transistor having drain and source terminals for connection to respective power supply rails and a gate terminal for receiving an input signal, the circuit further comprising a diode, having its anode connected to the gate terminal of the transistor and its cathode for connection to a bias voltage source, wherein the diode is arranged such that when the circuit is in use, the voltage level of the gate terminal of the field effect transistor is maintained at or below a predetermined value.
According to a second aspect of the present invention, there is provided a method of biasing a field effect transistor having drain and source terminals for connection to respective power supply rails and a gate terminal for receiving an input signal, the method comprising:
arranging a diode such that its anode is connected to the gate terminal of the transistor and its cathode is connected to a bias voltage source, the diode being arranged such that when the circuit is in use, the voltage level of the gate terminal of the field effect transistor is maintained at or below a predetermined value.
In a preferred embodiment, this allows the transistor to be readily turned off, using the available supply voltage, without requiring as many additional components as in the prior art circuits.
REFERENCES:
patent: 3655996 (1972-04-01), Takahashi
patent: 5363058 (1994-11-01), Sasaki
patent: 5438298 (1995-08-01), Hori
patent: 5506544 (1996-04-01), Staudinger et al.
patent: 5724004 (1998-03-01), Reif et al.
patent: 3920871 A1 (1990-08-01), None
patent: 0033 198 A1 (1981-08-01), None
patent: 0472340 A1 (1992-02-01), None
patent: 0473 299 A2 (1992-03-01), None
patent: 0691742 A2 (1996-01-01), None
patent: 0734 118 A1 (1996-09-01), None
patent: 55-109007 (1980-08-01), None
patent: 60-4866 (1985-01-01), None
patent: 62-114325 (1987-05-01), None
patent: 3-49403 (1991-03-01), None
patent: 61-296804 (1996-12-01), None
patent: WO 90/14712 (1990-11-01), None
patent: WO 91/16764 (1991-10-01), None
Blaas, D-L; PCT International Search Report; May 5, 1999; pp. 1-3; In re: International Application No. PCT/EP98/08303.
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