JPS63306710A - Fet multivibrator circuit - Google Patents

Abstract

PURPOSE:To decrease the temperature dependancy of an oscillated frequency by using a temperature compensation diode so as to connect a gate and a drain of a couple of FETs forming a current source. CONSTITUTION:The oscillating frequency f0 of the circuit is expressed as fo=I/4 CphiB, where I is a drain current flowing through FETs Q3, Q4, C is the capaci tance of a capacitor C1 and phiB is a barrier potential of diodes D1, D2. When temperature raises, the potential phiB of the diodes D1, D2 is lowered and since the barrier potential phiB of the diode D5 is lowered similarly in this case, the gate potential of the FETs Q3, Q4 is lowered and the drain current I flowing to the FETs Q3, Q4 is lowered. That is, the increase in the oscillating frequency fo due to the reduction in the barrier potential phiB is cancelled by the decrease in the drain current I, then the temperature dependancy of the oscillating fre quency f0 is decreased.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides an F E
This relates to a T multivibrator circuit.

[Conventional technology]

FIG. 2 is a diagram showing a conventional FET multivibrator circuit.

In this figure, Q lp Q t is the source-coupled switch
The n-type FET, C, constituting Sochi is the FETQs-
Capacitors connecting both source terminals of Qs, Q3゜Q4
connects both terminals of the capacitor C1 with a source supply voltage #V, ,
(Voltage is also ■.) An n-type FE'r that serves as a current source connected to
, R1, R, are the load resistors of the F E TQ t and Q t (resistance values are also R,, R, respectively), D,, l),
L is the load resistor R□, a diode for limiting the voltage drop due to the R load, QSP Q@ is an n-type FET that constitutes a source follower, Qy, Qs are Oij I"E
”' Q Ip Q se SOX supply'r4 source■sJl
The n-type FE 'l', D, , D, which serve as the connected current sources, are diodes for level shift 1, and lower the output voltage note of the source follower section to reduce the n-type FE 'I' Q I
Supplied to the gate terminal of PQ*. , N1 to N4 are nodes, Vrosi Isymuka2 is the drain supply power supply (voltages are also Vool and Voo2, respectively), V aslp
V6. is a constant voltage power supply.Next, I will explain about one work.

F E 'l' Q s that constitutes a source coupling switch
-Q*, one of them is always in the on state and the other is in the off state.

First of all, F E 'l'' Q 1 is off and F E
Assume T Q * is on. F as a current source
ETQs.

Since current I always flows through Q4, at this time, current l flows through capacitor C1 from node N4 to node N3, and a current of 21 flows through FE'rQ*. F
'1≦'l' Q The drain potential of x is the load resistor +
1, by 211't,t! However, with respect to the barrier potential φ of the diode D2, the resistance value 1 (if the value of 2 is selected, l-' E
The drain potential of 'l'Q2 is clamped to Vbb□-φ.

Therefore, the source potential of FETQ6 is equal to the threshold voltage V of F E 'r Q a from the gate potential ■rere and -φ-.
The potential V bb 1-chi-V TH becomes lower by rH. At this time, the gate potential V of FET Ql (N- is lowered by the level shift diode D4, -3φm
VTH.

On the other hand, )' E TQ , 0) So X potential v(N
s ) (t, dropped by the current ■ flowing through the capacitor C1, but F E '1''Q1 no k-r-
From the potential Vtnt3φ--VTH, F E 'l' Q
, the threshold voltage V TI4 is lower than the potential VDDI
Tattoki to 3φ-2VvH, 1('E'I' Q
, switches to the on state.

Therefore, the gate potential of F E 'r Q s is V be
1 to VDDI-φ8, and the source potential of FETQ is V DD 1- V TM b' to V DD 1
$s V TH<C fall.

The gate potential V (Nt) of r・°E'rQ8 is from the level shift diode 1)sic, VDD 1-2 φII
- From -VTH to ■Oki, descend to -3φ Matoi-VTH. F
The source potential V (N 4) of ETQ is the capacitor C
1, it is clamped with a time constant that is sufficiently large compared to the switching time of the FET, so F E 'l' Q
Source potential VDDI-2φ■-2VT when x is on
Equal to H.

Therefore, FE'l'Q, switches to the off state.

F E TQ Tomika < 7 t Ruto, F' E 'l
'Q1ノ')' -1-The potential rises by φ-, and the potentials at both ends of the capacitor C are V (N s) and V (N
a) Hasot Sore Vel 3φ--2V THb
'ra V shu 1-2 dvs 2VTM, VDI) 1-2
φ@-2V T14 h' et Vbo 1-$-2VvH
(C rises.

With the above, the initially assumed FE T Q 1 is off, FE
This means that the on state of TQt has been switched.

From the above, the output voltages V (N 1), V (N *) of the source-coupled multivibrator circuit in Fig. 2 are
, the potentials across the capacitor C1 V (N4), V (N
3) and the voltage applied across the capacitor v (N4)
The waveform of −V (N3) versus time is as shown in FIG.

Here, the oscillation frequency f0 is determined by the capacitance C of the capacitor C1 and the current source of the source-coupled switch unit FE TQ s
, determined by the current value I flowing through Qa and the maximum amplitude voltage 2φ applied across the capacitor C1, -■! . −■ Teko four ・・・・・・・・・・・・・・・・・・
It is expressed as (1).

[Problems to be Solved by the Invention] In the conventional F E 'I' multi-vibration circuit as described above, the oscillation frequency f0 depends on the barrier potential φ-. There is a problem in that the oscillation frequency 10 increases as the sun gets lower.

This invention was made to solve this problem, and the oscillation frequency has a small temperature dependence.
``The purpose is to obtain a multivibrator circuit.

[Means for solving problems]

The FET multivibrator circuit according to the present invention has a gate and drain of a pair of FETs constituting a current source connected by a temperature compensation diode.

[Effect]

In this invention, as the temperature rises, the barrier potential of the temperature compensation diode connected between the gate and drain of a pair of NETs constituting the current source decreases, and the tl current supplied by the current source decreases. becomes smaller.

〔Example〕

FIG. 1 is a diagram showing an embodiment of the FET multivibrator circuit of the present invention.

In this figure, the same symbols as in Fig. 2 indicate the same parts,
DS is a temperature compensation diode connected between the gate and drain of a pair of FETs forming a current source. R is a bias resistor, FE"' Q s -Q
40 both gate terminals are connected to a constant voltage power supply v, 1. Connect to □.

Next, the operation will be explained.

The oscillation frequency 10 of the FET multivibrator circuit shown in Fig. 1 is also the same as the oscillation frequency f0 of the conventional )=' E '1'' multivibrator circuit shown in Fig. 2<m<1
＞It is expressed by the formula, and when listed, it becomes -■ ``-4E7 stone ``'''''Old...Mountain...+11.

Here, l is FETQ3. Drain current value flowing through Q4, C is capacitance value of capacitor C, φ- is diode D
1, D is the barrier potential of 11.

Now, when the temperature rises, the diode D1. D! The barrier potential φ- of the diode 1]s decreases, but at this time the barrier potential φ- of the diode 1]s also decreases, so I"E'l"Q3-
The gate voltage of Q4 decreases and F E TQ 3pQ4
The drain current value I flowing through the drain current decreases.

That is, the 91-minute increase in the oscillation frequency of 1° due to the low barrier potential φ is offset by the low drain current value l, so that the temperature dependence of the oscillation frequency 10 becomes small.

The temperature coefficient of barrier potential φ removal is 41. vs, d, ■,
The drain current value l in the saturation region of the FET is expressed as: 1:K (V s V tn ) "..."---
It is expressed as (2).

However, ■, is the gate voltage, vvn is the threshold voltage, K
is the coefficient.

In FIG. 1, since the gate voltage V is equal to the barrier potential φ, equation (2) becomes 1=K(φken−VTH)2 ・−・・・・(2)′3.Now, Assuming that the temperature coefficient of the threshold voltage VTH is l' smaller than the temperature coefficient of the barrier potential φ-, the temperature coefficient of the drain current ■ can be expressed as follows. Yen/d'r...(3),
The temperature coefficient of the oscillation frequency f0 is 0/dT=-5LT! −/dT−+/dT=ThぢI
to·? /dT...(4)

Therefore, if you choose vTM=-φ■, the oscillation frequency f0
The temperature coefficient of the conventional F E '1' multipiflator circuit is 14-9 /
d rit can be reduced by a factor of 1.

In the above embodiment, one diode D, , D, was provided to limit the voltage drop, but two diodes!
One or more may be connected in series.

Similarly, each diode D8. D4. Similarly, two or more D can be connected in series.

〔Effect of the invention〕

As explained above, in this invention, the gate 1- and the drain of the pair of FETs constituting the current source are connected by a temperature-compensating diode. This has the effect of being able to compensate and reduce the temperature dependence of the oscillation frequency.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the FET multivibrator circuit of the present invention, FIG. 2 is a diagram showing a conventional F" E 'I" multivibrator circuit, and FIG. 3 is a diagram showing an example of the conventional FET multivibrator circuit shown in FIG. It is a diagram showing the internal voltage waveform in the FET multi-pipe circuit. In the figure, Q□~Q are FET, Ru, ) (2
is the load resistor, R3 is the bias resistor, D□~D4 are the diodes, and D and t are the temperature? lIg! Diode for C
1 is a capacitor, and N1 to N4 are nodes. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent Masuo Oiwa (2 others) Figure 1 Figure 2

Claims (1)

[Claims] A current source consisting of a pair of FETs whose gates and drains are connected in common is connected to a source-coupled switch, and a diode is arranged so that its barrier potential acts as a parameter that increases the oscillation frequency as the temperature rises. 1. A FET multivibrator circuit comprising: a gate and drain of a pair of FETs constituting the current source are connected by a temperature compensation diode.