JPS6129215A - Analog switching circuit - Google Patents

Abstract

PURPOSE:To widen dynamic range and make distortion of switch output voltage small by floating switch control voltage of a solid switching element of MOSFET etc. according to switch input voltage. CONSTITUTION:Switch control voltage phi1 that floats according to switch input voltage Vin is outputted from a modulating circuit 3. This switch control voltage phi1 is given to the gate of a switching MOSFET. As switch control coltage is floated according to switch input voltage, bias condition of FETS1 can be kept constant irrespective of amplitude of switch input voltage. Thus, switch input of large voltage amplitude can be transmitted faithfully always at a fixed condition. Accordingly, dynamic range can be widened, at the same time, distortion of switch output voltage can be made small.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a technology that is effective when applied to switch circuit technology and even analog switch circuits. This article relates to techniques that are effective for use in analog switch circuits.

[Background technology]

For example, as described in the Practical Electronic Circuit Handbook (pages 21221-227) published by CQ Publishing on October 20, 1975, analog switch circuits are constructed using solid state switching elements such as MOS field effect transistors. be able to.

This analog switch circuit has a wide range of applications, such as sample-and-hold circuits, Chirotsuba amplifier circuits, and switched capacitor filters.

However, in analog switch circuits using solid-state switching elements such as MOS field-effect transistors, when the amplitude of the switch input voltage becomes large, the bias condition of the solid-state switching element fluctuates greatly due to the large-amplitude input voltage. The inventors have found that a problem arises in that the waveform of the switch output voltage Vo is distorted.

[Purpose of the invention]

An object of the present invention is to maintain the bias condition of a solid-state switching element constant regardless of the amplitude of the switch input voltage. The present invention provides an analog switch circuit technology that enables faithful transmission, widens the dynamic range, and reduces distortion of the switch output voltage.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Summary of the invention]

A brief overview of typical inventions disclosed in this application is as follows.

That is, by floating the switch control voltage of a solid state switching element such as a MOS field effect transistor in accordance with the switch input voltage, the bias condition of the solid state switching element can be kept constant regardless of the amplitude of the switch input voltage. This makes it possible to faithfully transmit even switch input signals with large voltage amplitudes under constant conditions, widening the dynamic range and reducing distortion of the switch output voltage. This achieves the purpose of making it possible to make it smaller.

〔Example〕

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

In the drawings, the same reference numerals indicate the same or similar parts.

FIG. 1 shows the first analog switch circuit according to the present invention.
An example is shown.

The analog switch circuit shown in the figure is used in the tenbling circuit section of the sample and hold circuit. This analog switch circuit is constructed using a solid-state switching element whose conduction is controlled by voltage, and the switch control voltage φ1 of the solid-state switching element is set to the switch input voltage Vin. It is characterized by floating according to the

Therefore, an n-channel MOS field effect transistor S1 is used as the solid-state switching element.

The analog switch power Vtn is applied via the voltage follower 1 to the switch input side of the switch MOSt field effect transistor S1. M for this switch
The switch output voltage Vo passed through the OS field effect transistor S1 is applied to the hold capacitor C1. The voltage once held in this hold capacitor C1 is outputted via the voltage follower 2.

In addition, the above-mentioned switch MOS field effect transistor S1
The switch control voltage φ1 is set as the switch input voltage Win
A modulation circuit 3 is provided as a means for floating in accordance with. This modulation circuit 3 includes npn bipolar transistors Qll and Q21, a constant current circuit 41, and a resistor R.
11. It is composed of a C-MOS (complementary MOS) field effect transistor mlLm12, etc., and is operated by the power supply Vcc. This modulation circuit 3 uses the switch input voltage Vin as a modulation input, and uses the sample and hold pulse φO as a modulated input. From the output, a switch control voltage φl is obtained by changing the envelope voltage of the sample and hold pulse φO depending on the switch input voltage Vo.
is output. In other words, a switch control voltage φ1 that floats depending on the switch input voltage Vin is output. This switch control voltage φ1 is applied to the gate of the switch MOS field effect transistor S1.

FIG. 2 shows an example of the operation of the analog switch circuit shown in FIG. 1 using a waveform chart.

In FIG. 2, VpM is the switch input voltage vin
VpL indicates the maximum value, and VpL indicates the minimum value. vh indicates a voltage width that is necessary and sufficient to reliably turn ON (conducting) 10FF (non-conducting) the above-mentioned switch MOS field effect transistor S1. The switch control voltage φ1 is the voltage obtained by adding the above voltage width Vh to the switch input voltage Vin (
The amplitude is controlled so that it becomes (Vin+Vh). Then,
The width of the gate voltage, that is, the control voltage, relative to the switch input side of the switch MOS field effect transistor S1 is, for example, when the switch input voltage Vin is the maximum value V.
Even when taking pM or taking the lowest value VpL, the voltage width vh is always kept constant. As a result, the bias condition of the switching MOS field effect transistor S1 is always kept constant regardless of changes in the switch input voltage Vin and even if the voltage Vin has a large amplitude. As a result, the conduction state transfer characteristic of the switch MOS field effect transistor S1 is always constant, and a distortion-free switch output voltage 0 can be obtained even for a large amplitude switch input voltage Vin. .

The voltage width Vh of the DC component tb in the modulated output of the modulation circuit 3 can be arbitrarily set by selecting the Zener voltage of the Zener diode Dll inserted in the circuit 3.

FIG. 3 shows another embodiment of the modulation circuit section.

As shown in the figure, a large number of switch control voltages φ1. φ1. ..., npn bipolar transistor Qn, resistor Rn
, C-MOS field effect transistors l'm11, m21
By simply adding the switch control voltage φ1. φ2. ... can be obtained. This allows the aforementioned analog switch circuit to be replaced with a large number of analog switch circuits, such as switched capacitor filters.
Even when applied to a circuit using a switch, the present invention can be handled with a relatively small increase in the number of parts.

Note that the resistors Rn I Rn *... in FIG. 3 are connected to each control voltage φ1. φ1. This is for setting the amplitude levels of...

Figure 4: Second analog switch circuit according to this invention
An example is shown.

In the embodiment shown in the figure, a p-channel MOS field effect transistor is used as the solid state switching element.
I am using 7 star S2. To cope with this, the modulation circuit 3 is basically the same as that shown in FIG. 1, and includes bipolar transistors Q12. Q22, constant current circuit 42
, Zener diode D12, resistor R12, C-MOS
Although it is composed of field effect transistors m12+m22, etc., the transistor Q12. pnp in Q22
type is used. And in this case, the fifth
As shown in the figure, a switch control voltage φ2 having an amplitude with reference to the power supply Vcc is output.

FIG. 6 shows the third analog switch circuit according to the present invention.
An example is shown.

In the embodiment shown in the figure, the solid-state switching elements include an n-channel MO5 field effect transistor S1 and a p-channel MO5 field effect transistor S1.
A so-called C-MOS transmixer 9 in which a channel MOS field effect transistor S2 is connected in parallel.
is used. MOS field effect transistor 81 for each switch. S2 are switch control voltages φ1 . The conduction is controlled by φ2. The modulation circuit 3 is an n-channel MO
The switch control voltage φ1 of the S field effect transistor S1 and the switch control voltage φ2 of the p channel MOS field effect transistor S2 are outputted complementary to each other. The part for controlling the switch of the n-channel MOS field effect transistor S1 is the same as that shown in FIG.
Bipolar transistors Qll, Q21, Q2
4, constant current circuit 41, Zener diode Dll, C-
MOS field effect transistor mll+m21, resistor R1
1 etc. Also, p-channel MOS
The part that switches and controls the field effect transistor S1 is
Similar to that shown in FIG. 4, a pnp bipolar transistor Ql 2. It is composed of Q22°Q23, a constant current circuit 42, a Zener diode D12, a C-MOS field effect transistor m12°m22, a resistor R12, and the like. Accordingly, both MOS field effect transistors Sl.

Both S2 are ON (conducting) 1 under constant bias conditions.
It is designed to be driven to 0FF (non-conducting).

〔effect〕

(By floating the switch control voltage of a solid state switching element such as a MOS field effect transistor according to the switch input voltage, the bias condition of the solid state switching element can be kept constant regardless of the amplitude of the switch input voltage. As a result, even switch input signals with large voltage amplitudes can be faithfully transmitted under constant conditions, and the distortion of the switch output signal voltage can therefore be reduced. .

(2) Along with this, the effect of widening the dynamic range can be obtained.

Although the invention made by the present inventor has been specifically explained above based on Examples, it is to be noted that this invention is not limited to the above Examples and can be modified in various ways without departing from the gist of Section 7. Not even. For example, the solid state switching element may be a junction field effect transistor or other voltage controlled switching element.

[Application field]

In the above explanation, the invention made by the present inventor was mainly applied to analog switch technology for sample-and-hold circuits, which is the background field of application, but the invention is not limited to this, for example,
Analog equipment used in DBM (double balanced modulator) etc.
It can also be applied to switch technology. It can be applied at least to conditions that use switching elements whose transfer characteristics change depending on bias conditions.

[Brief explanation of drawings]

FIG. 1 shows the first analog switch circuit according to the present invention.
2 is a waveform chart showing an example of the operation of the circuit shown in FIG. 1; FIG. 3 is a circuit diagram showing another example of a portion of the circuit shown in FIG. 1; FIG. is the second analog switch circuit according to the present invention.
A circuit diagram showing an example,
1. FIG. 5 is a waveform chart showing an example of the operation of the circuit shown in FIG. 4, and FIG. 6 is a waveform chart showing an example of the operation of the circuit shown in FIG.
Circuit Diagram Showing the Embodiment FIG. 7 is a waveform chart showing an example of the operation of the circuit shown in FIG. 81.82... Solid state switching element (MOS electric, field effect transistor), 1.2... Voltage follower, 3... Modulation circuit, 41.42... Constant current circuit,
Dll, D12-... Zener diode, m11゜m
12...n-channel MOS field effect transistor,
m 211m 22...p channel MOS field effect transistor, Qll, Qn...npn bipolar transistor, Q12...pnp bipolar transistor, R11, R12, Rn-...resistance, Vin"
・Input signal voltage, φ0...sample hold pulse,
φ1. φ2...Switch control voltage, vo...Switch output voltage, Vcc...Power supply. Figure 1 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. An analog switch circuit configured using a solid-state switching element whose conduction is controlled by voltage,
An analog switch circuit characterized in that the switch control voltage of the solid state switching element is floated according to the switch input voltage. 2. The analog switch circuit according to claim 1, wherein the solid state switching element is a MOS field effect transistor.