JPS6224970Y2 - - Google Patents

Description

[Detailed explanation of the invention] This invention is a simple circuit that can stably connect the gate of MOSFET in an amplifier using MOSFET.
The present invention relates to a bias circuit capable of applying a bias between sources.

As is well known, MOSFETs have high input impedance characteristics, so almost no current flows through their inputs. Therefore, when applying a reverse bias to the gate, insert a resistor between the source and ground.
A reverse bias voltage is obtained by this voltage drop.

However, when the power supply voltage is low, the reverse bias voltage is a major factor in reducing the power supply utilization rate. For example, supply voltage 35V using 2SK176
For a gate reverse bias voltage in an amplifier of approximately −
It will account for 3V and nearly 10%. To avoid this, it is necessary to provide a separate power supply and supply a separate voltage, which makes the circuit complicated, expensive, and increases the failure rate.

This idea was made in order to eliminate the above-mentioned drawbacks of the conventional methods. It detects and rectifies a part of the high frequency signal (hereinafter referred to as RF signal) and smooths it, and then flows a current through the resistance between the gate and source of the MOSFET. An object of the present invention is to provide a bias circuit that can obtain a stable bias with a simple circuit by obtaining a reverse bias voltage.

Embodiments of the bias circuit of this invention will be described below with reference to the drawings. The figure is a circuit diagram showing the configuration of one embodiment. The illustrated embodiment shows an example in which the present invention is applied to a class D push-pull amplifier circuit.

In the figure, T ₁ is a transformer, one end of whose primary winding P ₁ is grounded, and the other end connected to the input terminal t ₁ . An RF signal is applied between input terminal _t1 and ground. Both ends of the secondary winding S ₁ of the transformer T1 are connected to the gates of MOSFETs Q ₁ and Q ₂ . Both ends of this secondary winding _S1 are each resistor
It is grounded via Rgs ₁ and Rgs ₂ , and these resistors Rgs ₁ and Rgs ₂ form a DC return circuit.

In addition to the above secondary winding S ₁ , the transformer T ₁ includes:
It has another secondary winding S ₂ and the secondary winding S ₁
has a center tap. This midpoint tap is grounded via a smoothing capacitor _C1 , and also via a rectifier diode _D1 and a secondary winding _S2 connected in series.

Each drain of MOSFETQ ₁ , Q ₂ is connected to output transformer T ₂
is connected to both ends of the primary winding _P2 . DC power E ₁ is supplied from the midpoint of this primary winding P ₂ , and one end of the secondary winding S ₂₂ of transformer T ₂ is grounded and the other end is connected to output terminal t ₂ . has been done.

Next, the operation of the bias circuit of this invention constructed as above will be explained. First, when an RF signal is applied between the input terminal _t1 and the ground, a signal opposite in phase to the RF signal is induced across the secondary winding _S1 of the transformer _T1 . This negative phase signal is MOSFETQ ₁ ,
MOSFETs Q _{1 and} Q ₂ amplify this anti-phase signal and output it to both ends of the primary winding S ₂₂ of transformer T ₂ , and then to the secondary winding S ₂ of transformer T 2. The amplified RF signal is taken out from the output terminal _t2 connected to ₂₂ .

At this time, the transformer T ₁ is also provided with a secondary winding S ₂ , and the voltage induced in the secondary winding S ₂ is rectified by the diode D ₁ , smoothed by the smoothing capacitor C ₁ , and the DC voltage is A bias is applied between the gates and sources of MOSFETs Q ₁ and Q ₂ from both ends of the secondary winding S ₁ to only the component from the intermediate tap of the secondary winding S ₁ . This enables MOSFETs Q ₁ and Q ₂ to operate, and amplifies the negative phase signal of the above-mentioned RF signal.

As described above, according to the bias circuit of this invention, two secondary windings are provided in the transformer, the RF signal induced in the first secondary winding is applied to the gate of the MOSFET, and the RF signal is applied to the gate of the MOSFET. After rectifying and smoothing the RF signal induced in the secondary winding, only the DC component is applied as a bias between the gate and source of the MOSFET through the first secondary winding, so with a simple circuit configuration, A stable bias can be provided. Moreover, since the circuit configuration is simple, it can be made at low cost.

[Brief explanation of the drawing]

The figure is a circuit diagram showing an embodiment of the bias circuit of this invention. T ₁ , T ₂ ... Transformer, t ₁ ... Input terminal, t ₂ ... Output terminal, P ₁ , P ₂ ... Primary winding, S ₁ , S ₂ , S ₂₂ ...
Secondary winding, D ₁ ... diode, C ₁ ... smoothing capacitor, Q ₁ , Q ₂ ... MOSFET, Rgs ₁ , Rgs ₂ ...
…resistance.

Claims (1)

[Scope of utility model registration request] The first step is to apply a high frequency signal to the gate of the MOSFET.
and a transformer having a second secondary winding, and a high frequency signal induced in the second secondary winding of this transformer is rectified and smoothed to convert only the DC component into the first transformer. above through the secondary winding of
A bias circuit consisting of a circuit that applies a bias voltage between the gate and source of a MOSFET.