JPH0549124B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a common mode output circuit, and more particularly to a common mode output circuit with gain.

[Conventional technology]

Conventionally, this type of circuit has N
The gate of the channel MOSFET11 is input, the drain is connected to the power supply, the source is connected to the ground potential via the load element I11, and the N-channel
A source follower circuit in which the source of MOSFET 11 is used as an output is known. Curve C in FIG. 3 shows the input/output characteristics of this circuit, and it can be seen that this circuit has no gain. Therefore, this circuit can only be used as a level shifter that changes the DC level between input and output signals, or as an impedance converter.

On the other hand, there is also a method of connecting two stages of inverting amplifiers A1 and A2 in series, as shown in FIG.
This method can be expected to yield quite high profits, but
Since the phase delay of the signal also doubles, a phase compensation circuit is required. However, since this method means narrowing the frequency band of the second stage, the frequency band of the entire amplifier also becomes narrow.

[Problem that the invention seeks to solve]

In the conventional source follower circuit described above, even if an in-phase output is obtained, the gain is less than 1. Further, a circuit in which two stages of inverting amplifiers are connected in series has a drawback that, although it has sufficient gain, the frequency band is narrow and it cannot handle high frequency signals.

Therefore, an object of the present invention is to provide an in-phase output circuit with sufficient gain and a wide frequency band.

[Means for solving problems]

The in-phase output circuit of the present invention has an input terminal that receives an input signal, and a first terminal that supplies a first power supply potential.
a second power supply terminal for supplying a second power supply potential; a first transistor of one conductivity type having a gate electrode connected to the input terminal and a drain electrode connected to the first power supply terminal; , a second transistor having a conductivity type opposite to that of the first transistor, the source electrode of which is connected to the source electrode of the first transistor and whose gate electrode receives a control voltage; and a drain electrode of the second transistor connected to one end thereof. and an output terminal connected to a connection point between the drain electrode of the second transistor and the load element to receive an output signal. .

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

Referring to FIG. 1 showing a circuit diagram of a common mode output circuit according to a first embodiment of the present invention, this common mode output circuit includes an N-channel MOSFET 1 whose gate is connected to the input and whose drain is connected to the power supply, and whose source is connected to the N-channel MOSFET 1.
Connect the source of MOSFET1 and the gate to the voltage source V _B
P-channel MOSFET2 connected to
This configuration includes a load element I1 connected to the drain of the channel MOSFET 2 and the other end connected to the ground potential. Also, this common mode output circuit is a P channel.
The configuration is such that the output is output from the connection point between the drain of MOSFET 2 and the load element I1.

Next, the operation of the common mode output circuit according to the first embodiment of the present invention will be explained with reference to curve A in FIG. 3 showing the characteristics of the common mode output circuit according to the first embodiment of the present invention.

First, when the input is at a low level (hereinafter abbreviated as "0"), the N-channel MOSFET 1 is in an off state, and the output is also "0". When the input signal rises from "0" to turn on the N-channel MOSFET 1, the source potential of the N-channel MOSFET 1 and the source potential V _A of the P-channel MOSFET 2 also rise from "0". However, the P-channel MOSFET 2 has a substrate effect and does not easily turn on. Moreover, N-channel MOSFET 1 is also affected by the substrate effect as the source potential increases, so it can be turned on sufficiently and the source potential
Only V _A increases with increasing input signal.

At this time, since the P-channel MOSFET 2 is not in the on state, the output continues to be "0". Furthermore, the input signal continues to rise, and finally the P channel
When MOSFET2 is turned on, these N
Channel MOSFET1 and P channel
If MOSFET2 is designed to have a lower DC impedance than load element I1, the output will rise rapidly. Gain can be obtained by biasing an input signal to this portion.

Next, when the input signal approaches the High level (hereinafter abbreviated as "1") side, the N channel
Both MOSFET 1 and P-channel MOSFET 2 are fully turned on, and this in-phase output circuit has DC impedance sufficiently lower than that of load element I1, so that it has the same characteristics as the source follower circuit of the prior art. Here, P channel
Voltage V _B biasing the gate of MOSFET2
The operating point of this circuit can be adjusted by changing the threshold voltage of P-channel MOSFET2,
In other words, the point at which the output rises from "0" can be changed.

In addition, in an inverting amplifier circuit, the Miller capacitance added between the input and output determines the upper limit of the frequency band.
The common mode circuit works to compensate for the decrease. Therefore, the in-phase output circuit of the present invention, which has a circuit configuration of a combination of a source follower circuit and a common gate circuit, exhibits good characteristics in a high frequency region.

Next, a common mode output circuit according to a second embodiment of the present invention will be explained.

Referring to FIG. 2, which shows a circuit diagram of the common-mode output circuit of the second embodiment, the common-mode output circuit of the second embodiment includes an N-channel MOSFET 21 whose gate is connected to the input and whose drain is connected to the power supply; N
P-channel MOSFET 22 connected to the source of channel MOSFET 21, and one end connected to the P-channel MOSFET 21.
A load element I21 connected to the drain of MOSFET22 and the other end connected to ground potential, and an N-channel
MOSFET21 and P-channel MOSFET22
The configuration includes an inverting amplifier A3 that inputs the potential V _S at the connection point of each source of and connects its output to the gate of the P-channel MOSFET 22.
Furthermore, it is configured to output from the connection point between the drain of the P-channel MOSFET 22 and the load element I21.

That is, in the first embodiment, the gate of the P-channel MOSFET 2 connected between the N-channel MOSFET 1 and the load element I1 of the source filter circuit was biased with a constant voltage V _B , but in the second embodiment, the in-phase In the output circuit, N-channel MOSFET2
The potential V _S at the connection point of the respective sources of MOSFET 1 and P channel MOSFET 22 is input to the inverting amplifier A3, and the output of the inverting amplifier A3 is input to the P channel MOSFET.
It is added to the gate of MOSFET22.

Next, the operation of the common mode output circuit according to the second embodiment of the present invention will be explained with reference to curve B in FIG. 3 showing the characteristics of the common mode output circuit according to the second embodiment of the present invention.

When high voltage is applied to the input, N-channel MOSFET
When the potential V _S at the connection point of the sources of each of P-channel MOSFET 21 and P-channel MOSFET 22 is higher than the threshold voltage of inverting amplifier A3, P-channel MOSFET 2
The gate of 2 is “0” and P channel MOSFET 22
turns on sufficiently and attempts to pull down the potential V _S at the connection point to the "0" side.

On the other hand, when the input voltage becomes low and the potential V _S at the connection point becomes lower than the threshold voltage of the inverting amplifier A3, the output of the inverting amplifier A3 changes to "1" and acts to turn off the P-channel MOSFET 22.

In this way, the potential V _S at the connection point is controlled so that it does not fall below a certain level, and as a result,
The substrate effect voltage of the N-channel MOSFET 21 is maintained at a high value, and the change point shifts to a higher value as shown by curve B in FIG. When the input voltage is high, N-channel MOSFET21 and P-channel
The MOSFET 22 is fully turned on and has the same level as a normal source follower circuit.

Therefore, a common mode output circuit with higher gain can be realized.

〔Effect of the invention〕

As described above, the present invention can realize a circuit having gain in the same phase by providing a transistor of a conductivity type opposite to that of the driving transistor between the driving transistor and the output of the conventional source follower circuit.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 show the first and second embodiments of the present invention.
FIG. 3 is an input/output characteristic diagram of the common-mode output circuit, and FIGS. 4 and 5 are circuit diagrams of the common-mode output circuit of the prior art. 1, 11, 21...N channel MOSFET,
2, 22...P channel MOSFET, I1, I1
1... Load element, A1, A2, A2... Inverting amplifier, V _B ... Voltage source, V _A , V _S ... Potential at source connection point, V _DD ... Power supply potential.

Claims (1)

[Claims] 1. Connecting the input terminal to an input terminal receiving an input signal, a first power supply terminal supplying a first power supply potential, a second power supply terminal supplying a second power supply potential, and a gate electrode. The drain electrode has the first
a first transistor of one conductivity type to which the power supply terminal of the first transistor is connected, and a second transistor of a conductivity type opposite to that of the first transistor whose source electrode is connected to the source electrode of the first transistor and whose gate electrode receives a control voltage. a load element having one end connected to the drain electrode of the second transistor and the other end connected to the second power supply terminal, and a connection point between the drain electrode of the second transistor and the load element; An in-phase output circuit characterized by comprising an output terminal to which the output terminal is connected and receives an output signal.