JPS60103811A - Current mirror - Google Patents

Abstract

PURPOSE:To attain current mirror operation with excellent frequency characteristic by providing a signal transmission circuit comprising a differential amplifier and an emitter follower or the like between the input circuit and the output circuit of a current mirror circuit consisting of an L-PNP transistor (TR). CONSTITUTION:An input signal Vin is fed to a base of a TRQ11 via a terminal No.1. The input current Iin proportional to the input signal Vin flows to the L- PNP TRQ12 and the TRQ11 from a current +Vcc fed to a terminal No.2. A voltage VBEQ12 proportional to the Iin is produced across the Q12 as a load and a voltage +Vcc-VBEQ12 is applied to a non-inverting input terminal (+) of an operational amplifier 1 as a signal transmission circuit of high input impedance. On the other hand, since an output signal of the operational amplifier 1 is fed back negatively by 100% to the inverting input terminal, the operational amplifier 1 acts like a low output impedance voltage follower having the voltage gain 1. The provision of the said operational amplifier 1 prevents an AC impedance of the TRQ12 from giving effect on the base circuit of the TRQ12.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a current mirror, and particularly to a lateral PNP
Related to current mirrors using transistors.

[Background technology]

Current mirrors are widely used in various electronic devices, and there are many types of circuit configurations. Figure 1,
The circuits shown in FIGS. 2 and 3 are based on a known current mirror Q2. Q
3.

Here, in order to make the novel features of the present invention easier to understand,
The operation and characteristics of the stiff circuit will be explained.

In the circuit shown in FIG. 1, when an input signal Vin is supplied through the No. 1 terminal, an input side current Iin flows through the transistor QllQ2. Then, ■BE occurs in the transistor Q2, the transistor Q3 operates, and the output side current Ioot flows through the transistor Qs and the load RL. Note that the PNP transistor Q2+Q is a lateral PNP transistor (hereinafter referred to as an L-PNP transistor) formed within a semiconductor substrate.

In the current mirror circuit, transistor Q2.
The common emitter current gain of Q11 is hFEQ2.

If we calculate the current mirror ratio C using hFF and Q3, we find that it becomes fc.

Here, in the low frequency region, hFEQ2 and hFEQ3
``30 becomes 2, and at high frequency hFYQ2'' hFEQ
If 3 = 6, then C = - = 0.75 ・・・・・・・・・・・・・・・
・・・・・・・・・・・・ (You can see that it is 31.

Furthermore, the operation lower limit voltage V of the current mirror circuit is
When you set ccmin, "0m'n""CEQI I aa t l +
■BEQ2°−°−゛(It can be seen that it is determined by J.

The inventor's experiments revealed that the frequency characteristic of the current mirror circuit has a cutoff frequency of about 8 MH2. (See FIG. 1(B)) Regarding the circuit shown in FIG. 2, when the input signal Vin is supplied, the L-PNP transistor Q2. The base current of Q3, current is L-PNP) transistor Q, [flows.

A collector current is supplied to the transistor Q from the base of the L-PNP transistor Q and the collector of the transistor Q2. Therefore, as the input current Iin flows, the output current Ioot flows.

When calculating the current mirror ratio C in this current mirror circuit, it can be seen that from hFEQ3, from B, FEQ3 C=□ (5) hFKQ2 +□ hFEQ4+1.

Low frequency hFF, Q□, Q3. When Q4=30, the current mirror ratio C is 0.9978, and the high frequency hF□2.
It can be seen that when Q3°, 4=6, C becomes 0.9545.

In addition, the operating lower limit voltage Vccmin is vo””” ”” ■+-EQI l5atl +vB
EQ4 +VBEQ2=VCEQ1f88tl +2V
BE...-(61(""BEQ4"vBEQ
2 "" vBg).

Furthermore, looking at the frequency characteristics, the collector load of transistor Q is two L-PNP) transistors Q2. Q
4, and since these are L-PNP transistors, the phase delay t becomes large in the high frequency region, and as shown in Fig. 2(n), the inventor's experiments show that a peaking appears in the frequency characteristics near 9MH2. It was made clear by Therefore, when the input signal Vin reaches a frequency of 9MH2, a peak as shown in FIG. It was also found that the phenomenon was more likely to occur.

In addition, the transistor Q21Qs in the circuit shown in FIG.
The portion Qs is a well-known Wilson type current mirror circuit. It can be seen that when the current mirror ratio C is calculated, TE is determined. hFEQ2 at low frequencies
．． Q3. If Q5 is 0, the current mirror ratio C is 0.9979, and at high frequency hYPNP=
6, it can be seen that the current mirror ratio (Jjo, 96) is obtained. Also, the lower operating limit 'power supply load Vccmin' is determined by K as in the above equation (6), Vccmin =: VCEQI fsat ) +
2 VBE.Furthermore, looking at the frequency characteristics,
The collector load of transistor Q is three L-PNP transistors Q2, Qs, Qe and three L-PNP transistors. In this case, it has not been clarified by the inventor's actual work 1* that due to the phase delay iK of the three L-PNP) transistors, a peaking characteristic as shown in the 311th MI (Bl) appears near the cutoff frequency of 25MH2. .

It has also been found that the oscillation phenomenon tends to occur when the frequency of the input signal Vin is around 25 MH2.

[Purpose of the invention]

An object of the present invention is to provide a novel current mirror circuit that has a relatively large current mirror ratio, has no risk of oscillation, and can also be driven by a low voltage, piezoelectric power source. 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]

Among the inventions disclosed in this application, a brief summary of typical inventions is as follows.

That is, in a current mirror circuit using lateral PNP transistors on the input side and output side, a differential amplifier, an NPN transistor is used as a signal transmission circuit between the input side and the output side.
) An emitter follower circuit etc. consisting of a transistor is provided, and FL6 and two lateral P are used on the input side and the output side.
By isolating the NP transistors using this signal transmission circuit, the object of the present invention described in item 1 can be achieved.

[Embodiment 1] Hereinafter, a first embodiment of a circuit using a current mirror according to the present invention will be described with reference to FIG. 4 (At(B)).

The technical content will be explained below along with the circuit operation.

The input signal vin is connected to the transistor Q1 through the terminal 1.
1 base. The first +V supplied to the second terminal
From the cc current, the L-PNP transistor QI2. An input current Iin proportional to the input signal Vin flows through the transistors Q, , K. Q as a load, Ii between both ends of □
n K is proportional to "BEQ12", +vcc'BEiQ
A voltage of □2 is applied to the non-inverting input terminal (+) of the operational amplifier 1 as a signal transmission circuit with high input impedance. On the other hand, since the output signal of operational amplifier l has 100% negative feedback at its inverting input terminal, operational amplifier l has a vehicle pressure gain of 1.
operates as a low output impedance voltage follower.

Operational amplifier 1 consists of the base of L-PNP transistor QI2, which is the input end transistor of the current mirror, and the L-PNP transistor Q+, which is its output transistor.
It is provided to isolate the base of the s. By providing an operational amplifier l with high input impedance and low output impedance, the AC impedance of L-PNPh transistor QI3 becomes L-PNP)
There is also no effect on the base circuit of transistor Q12. Then, an output phase, voltage VO, corresponding to the input voltage supplied to the non-inverting input terminal (+) of the operational amplifier 1 can be obtained with low output impedance. The output voltage Void is supplied to the base of the L-PNP transistor QI3' and drives it.

As a result, an output current Ioot flows from the Vcc power supply to the I, -PNP) transistor Q+3 and the load RL.

The output voltage Voot is obtained by the load RL voltage drop.

Here, when the current mirror ratio C of the embodiment shown in FIG. 4 is calculated, it is determined as 11n hFEQ12 +1. At low frequencies, when both hFEs are 30, we obtain c-LQ-=0.9677. Also, when both hFEs are 6 in one wave of cylinder circumference, c = -L- = o, s 5714, and the high value is 6
It is clear that +1 can be obtained.

Furthermore, if the lower operating limit voltage Vccmin is decreased, Vccmi
n=”CF:Qll(sat)+yBEQ12°
It is clear that it becomes α2 and can be driven with low power source pressure.

Furthermore, what you should pay attention to is that the frequency characteristics are very good.

That is, L-PNP) transistor Q+2 + Q10
Both have a phase lag. However, since the transistors are isolated by the operational amplifier IVc, a feedback loop with a large phase delay is not formed. As a result, as shown in FIG. 4(B), no peaking characteristics appear in the high frequency portion (for example, around 15 MH2 to 20 MH2), resulting in extremely good frequency characteristics. Therefore, the oscillation phenomenon can be prevented from occurring without providing a peaking circuit or the like for flattening the Norr wave number characteristics.

[Embodiment 2] Next, a second embodiment of a circuit using a current mirror of the present invention will be described with reference to FIG. Note that components that perform the same circuit operations as those in the first embodiment are designated by the same reference numerals, and their explanations will be omitted.

In this embodiment, the performance amplifier 1 is constituted by biholer transistors Q21 + Q22, and a differential pair is provided. In this example, transistor Q
The base of □ serves as the non-inverting input terminal (+) of operational amplifier 1, and the transistor Ql! The base of 2 is an inverted input terminal ←)
As a result, the collector of the transistor Q22 operates as a cutting terminal, and since the output terminal and the inverting input terminal are directly connected, the operational amplifier 1 similarly operates as a voltage follower.

Therefore, in the current mirror circuit in the embodiment VC of FIG. 5, the output side is driven while being isolated from the input side, and the effect as described in the first embodiment of FIG. 4 can be obtained.

[Embodiment 3] Next, a third embodiment of a current mirror circuit to which the present invention is applied will be described with reference to FIG. The difference between this embodiment and the first and second embodiments is that the operational amplifier 1,
2, the emitter 7 consists of a transistor Q23 with high input impedance and low output impedance.
The reason lies in the fact that it has an orowa.

By supplying the input signal Vin, the input side current fin flows in the same manner as described above. Therefore, a voltage drop proportional to Iin occurs across diode-connected transistor Q230.

Furthermore, the base of the L-PNP transistor QI3 is connected to the transistor Q3. is supplied through the base-eminter junction of emitter follower transistor Q23. Then, a transistor Q24 and an L-PNP transistor QI3 are connected as a diode from the +Vcc power supply.
, load PLK input side turtle current n K proportional output current I
oot is played. The output voltage Voot is obtained by the voltage drop of the load RL.

Note that transistor Q24 is the same NPN transistor as transistor Q2B. Therefore, if the transistors Q23 w Q24 are manufactured in the same integrated circuit chip, the variations in various electrical characteristics and temperature changes of the transistors Q23 + Q24 will be equal to each other, and the influence on the current mirror ratio C of the transistor Q23 will be the same as that of the transistors. Sofi of Q24 can be canceled out.

Also in the current mirror circuit shown in this embodiment, the same effects as those described in the first and second embodiments can be obtained.

[Embodiment 4] Next, a fourth embodiment of a current mirror circuit to which the present invention is applied will be described with reference to FIG. Note that in this example,
A resistor R is added to the current mirror circuit described in the first embodiment.
8. A peaking circuit using a capacitor CI+ is provided, and the frequency bandwidth can be adjusted.

By supplying the input signal Min, the input side current I
in flows, and due to the circuit operation of operational amplifier 1, L-P
The NP transistor Q13 is the driving source.

And the parallel circuit of resistor R3 and capacitor, L-PN
The output side current Ioot flows through the P transistor QI3, and the output voltage Voot is obtained in the same manner as described above. On this occasion,
For high frequency input signal (1, resistor R3 + capacitor C
The impedance of the parallel circuit of 1 is essentially the capacitor c
determined by a small impedance of 1. Therefore, the common emitter voltage gain of the transistor Q13 at high frequencies increases, and peaking characteristics at high frequencies can be obtained.

Except for such peaking characteristics, the same effects as in the first embodiment can be obtained.

〔effect〕

(II L-PNP) By providing a signal transmission circuit such as a differential amplifier or an emitter follower between the input side circuit and the output side circuit of the FLft current mirror circuit composed of transistors, a current with good frequency characteristics can be achieved. The effect of performing a mirror operation can be obtained.

(2) The operating lower limit power supply voltage is the collector-emitter voltage V of the input transistor. Since the voltage is determined by the sum of E(satl and the forward type voltage between the base and emitter of the diode-connected transistor t'I, the current mirror operation is stable at a low power supply voltage. This effect can be obtained.

[Application field]

In the above description, the invention made by the present inventor was mainly applied to a current mirror circuit, which is the background field of application, but the invention is not limited thereto.

Since the frequency characteristics are good, it can be used in semiconductor integrated circuits for video equipment that use low power supply voltages.

Further, it can be used in various audio equipment such as a double tape recorder that uses a low power supply voltage.

Current mirror transistor Q12゜QCs of the present invention
is not limited to lateral PNPK.

It can also be applied to transistors with a large phase lag.

[Brief explanation of drawings]

11K(A) shows a circuit diagram of a circuit using a known current mirror, FIG.
) shows a circuit diagram using a known Fi current mirror, FIG. 2(B) shows a frequency characteristic diagram of the same as above, and FIG.
) shows a circuit diagram of a circuit using a known current mirror, FIG. 3 (B) shows a frequency characteristic diagram of the same as above, and FIG. 4 (A
) shows a circuit diagram showing the first embodiment of the circuit using the current mirror of the present invention, No. 4 1(B) shows a frequency characteristic diagram of the same, and FIG. 5 shows the circuit diagram of the second embodiment of the present invention. FIG. 6 is a circuit diagram showing a third embodiment of the present invention, and FIG. 7 is a circuit diagram showing a fourth embodiment of the present invention. QH+ QCs + QCs + Q21 + Q22
+ Q23 ''' Transistor, 1... Differential amplifier, 2... Operational amplifier, Vin... Input signal Ii
n...Input side current, Ioot...Output side current, VO
ot...output voltage, R1+ R2+ R3"'resistance,
C4... Capacitor, C8,... Constant voltage (-circuit,
RL...Load resistance, Vcc...Electric IM voltage, IC...
...Semiconductor integrated circuit. Agent Patent Attorney Akio Takahashi - “h, Fig. 1 Fig. 2 (A) (B) 1 (1f.7 / (g) (8 Nog Hnxr YMMl Procedural amendment (method) 2 Display of the case 1982 Patent application No. 210809 Name of the invention Person who performs current mirror correction Toy 'I and I' Patent applicant name I+' (510) Figure 2 bale CA) C- (8) nnt

Claims (1)

[Claims] 1. A signal transmission circuit with high input impedance is provided between the pace of an input transistor constituting the input side circuit of the current mirror and the base of the output transistor constituting the output side circuit of the current mirror. A current mirror that is characterized by: 2. The current mirror according to claim 1, wherein the signal transmission circuit is comprised of a voltage follower. 3. The current mirror according to claim 1, wherein the signal transmission circuit is an emitter follower composed of an NPN transistor.