JPH0363847B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical field to which the invention pertains) The present invention relates to an amplifier circuit, and in particular, to an amplifier circuit that cancels temperature changes in gain due to the temperature coefficient of mutual conductance of transistors in configuring a common emitter amplifier circuit. Regarding circuits.

(Prior Art) A grounded emitter amplifier circuit has better noise characteristics than a differential input type circuit, and is used in amplifier circuits and the like that require low noise characteristics.

FIG. 1 shows a conventional circuit example of a common emitter amplifier circuit, which is composed of transistors Q ₁ and Q ₂ , resistors R ₁ and R ₂ , and a constant current source CS ₁ . A base bias current is supplied to the base of the input first stage emitter-grounded transistor Q ₁ connected to the input terminal 1 by the resistor R ₁ . The collector of the transistor Q ₁ is connected to the load resistor R ₂ and the base of the output buffer transistor Q ₂ , and the emitter of the transistor Q ₂ is connected to the constant current source CS ₁ and to the output terminal 3. It is connected.

In this conventional circuit, the voltage gain G _V is expressed as G _V =gm·R _L (1), as is well known, and is obtained by the product of the load resistance R _L and the transconductance gm of the transistor. Here, the mutual conductance gm is given by gm=q/KT・I _C (2). However, q is the electron charge, K is Boltzmann's constant, T is the absolute temperature, and I _C is the collector current.

Furthermore, the collector current I _C is the base bias current supplied by the resistor R ₁ multiplied by the current amplification factor of the transistor Q ₁ , I _C = h _FEQ1 × (V _CC −V _BEQ1 /R ₁ ) …( 3). However, h _FEQ1 is transistor Q ₁
, V _BEQo is the forward bias base-emitter voltage of transistor number n, and V _CC is the power supply voltage.

Therefore, the voltage gain G _V of this conventional circuit is given by G _V = q/KT×h _FEQ1・(V _CC −V _BEQ1 /R ₁ )×R ₂ (4), where (q/KT), h Subject to gain variations due to variations in _FE , V _BE , R ₁ , and R ₂ .

FIG. 2 shows a conventional circuit example of a common emitter amplifier circuit that suppresses such variation factors and stabilizes the bias.

In FIG. 2, the collector of the input first-stage grounded emitter transistor _Q10 is connected to a load resistor _R10 , and is also connected to the base of an output buffer transistor _Q11 . The emitter of the transistor _Q11 is connected to the output terminal 12, the resistor _R11 , and the base of a transistor _Q12 whose emitters are commonly connected to the transistor _Q13 to form a differential circuit.
The collectors of the differential transistors Q ₁₂ and Q ₁₃ are connected to active loads composed of transistors Q ₁₄ and Q ₁₅ , respectively, and the commonly connected emitters are connected to the power supply terminal 11 via a constant current source CS _2. .
On the other hand, there is a resistor at the base of the differential transistor _Q13 .
The voltage provided by voltage division by R ₁₃ and R ₁₄ is level-shifted by transistor Q ₁₆ and is then provided as a reference voltage. The base of the first-stage transistor Q ₁₀ connected to the input terminal 10 is connected to the collector of the differential transistor Q ₁₃ via the feedback resistor _RF , and is supplied with a base bias current, as well as the differential transistors Q ₁₂ , Negative DC feedback is applied by capacitor C and feedback resistor _RF so that the base potential of _Q13 is balanced. Here, the capacitor C is for bypassing the alternating current component and applying negative direct current feedback to the base of the transistor _Q10 .

In the circuit shown in FIG. 2, the voltage gain G _V1 is expressed as G _V1 = gm·R ₁₀ (5). Here, gm is the mutual conductance of the transistor _Q10 , and is expressed as gm=q/KT·I _C (6). Here, I _C is the collector current of transistor Q ₁₀ .

On the other hand, the potential difference V _R10 across the resistor R ₁₀ is equal to the potential difference across the resistor R ₁₃ because the base potentials of the transistors Q ₁₂ and _{Q 13 are equal} ;
With the power supply voltage V _CC , it is given by V _R10 = R ₁₃ / R ₁₃ + R ₁₄ V _CC (7). Therefore, the collector current I _C of the transistor Q ₁₀ is I _C = V _R10 /R ₁₀ = R ₁₃ /R ₁₀・1/(R ₁₃ + R ₁₄ )V _CC ……
Gain G _V1 given by (8) is given by (5), (6), and (8), G _V1 = q/KT・R ₁₃ / (R ₁₃ + R ₁₄ )・V _CC ……(9) It will be done. Therefore, the gain G _V1 is determined by the relative ratio of the resistances and is stable, but since it has a term expressed by (q/KT), it has a temperature coefficient and the gain fluctuates due to temperature fluctuations.

(Objective of the Invention) The object of the present invention is to provide a common emitter amplifier circuit that suppresses the effects of variations in resistance and current amplification factor h _FE in addition to the conventional circuit that suppresses the effects of variations in resistance and current amplification factor hFE. An object of the present invention is to provide an amplifier circuit that cancels out the term , and obtains a stable gain even with temperature fluctuations.

(Structure of the Invention) The amplifier circuit of the present invention has a base connected to an input terminal, an emitter connected to a ground potential, a collector connected to a power supply via a first resistor, and a first amplifier circuit connected to an output terminal. a transistor; a diode having an anode connected to a reference current supply circuit and a cathode connected to a ground potential; a base connected to the anode of the diode, an emitter connected to the ground potential via a second resistor, and a collector connected to a third resistor; a second transistor connected to a power supply through a resistor, detecting a potential difference between a DC potential of a collector of the second transistor and a DC potential of a collector of the first transistor, and equalizing both DC potentials; and negative feedback means to the input terminal.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 3 is a circuit diagram of one embodiment of the present invention. The same elements and terminals with the same functions as in FIG. 2 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

In Figure 3, the emitter of diode-connected transistor _Q18 is grounded and the transistor
The collector-base connection terminal of _Q18 has one end connected to the power supply terminal 11, the other end of the resistor _R16 constituting the reference current supply circuit, and the base of the transistor _Q17 . The emitter of transistor Q ₁₇ is grounded through resistor R ₁₅ ,
The collector of the transistor _Q17 is connected to the power supply terminal 11 via the resistor _R13 , and is also connected to the base of the transistor _Q16 .

In this example, the potential difference across the resistor _R10
V _R10 is the resistor R ₁₃ as in the circuit shown in Figure 2 above.
It is equal to the voltage V _R13 applied across the terminals and can be found as follows.

First, the reference current Iref flowing through transistor _Q18
is expressed as Iref=V _CC −V _BEQ18 /R ₁₆ (10). Next, the collector current I _CQ17 of the transistor Q ₁₇ is calculated from KT/qlnI _CQ17 /I _s +I _CQ17・R ₁₅ =KT/qlnIref/I _s (11), where Is is the saturation current of the transistor _. = 1/R ₁₅・KT/qlnIref/I _CQ17 ......(12) Here, the ratio of the reference current Iref to the collector current I _CQ17 of transistor _Q17 (Iref/I _CQ17 )
When is set as A, it is expressed as I _CQ17 = 1/R ₁₅・KT/qlnA (13).

Therefore, the potential difference V _R10 across the resistor R ₁₀ is expressed as V _R10 = V _R13 ] R ₁₃ ·I _CQ17 = R ₁₃ /R ₁₅ ·KT/qlnA (14). Therefore, the collector current I _C of the transistor Q ₁₀ is I _C = V _R10 /R ₁₀ = R ₁₃ /R ₁₀・R ₁₅・KT/qlnA =KT/q・B ……………(15) where , B=R ₁₃ /R ₁₀・R ₁₅・lnA, and the mutual conductance gm of transistor Q ₁₀ is given by equation (6): gm=q/KT・I _C =q/KT (KT/q・B) =B=R ₁₃ /R ₁₀・R ₁₅・lnA (16) It is obtained as follows, and the term (q/KT), which is the temperature coefficient, is canceled out in the mutual conductance equation.

Therefore, the gain G _V of the circuit example of the present invention is expressed as G _V1 = gm・R ₁₀ = R ₁₃ /R ₁₅・lnA (17) from equations (5) and (16), and the current The ratio A is determined by the ratio of resistors _R13 and _R15 , and the temperature variable (q/
KT) are canceled out.

Therefore, according to this embodiment, it is possible to provide a grounded emitter amplifier circuit whose temperature characteristics are significantly improved compared to the conventional one and whose gain is stable against temperature fluctuations.

Note that the present invention is not limited to this embodiment. For example, the transistor may be of a PNP type, the negative feedback means and the reference current generation circuit may be realized with other appropriate circuits, and the diode may also be formed of the same transistor as in the embodiment. Although it is more desirable to form a diode, a simple diode may also be used.

(Effects of the Invention) As explained in detail above, the amplifier circuit of the present invention has the above-described configuration, so that the term (q/KT), which is the temperature coefficient of the gain formula, can be canceled out. In addition to suppressing the influence of variations in current amplification factors of transistors, this has the effect of providing stable gain even with temperature fluctuations.

[Brief explanation of drawings]

1 and 2 are circuit diagrams of a conventional example, and FIG. 3 is a circuit diagram of an embodiment of the present invention. In the figure, 1, 10...input terminal, 2, 11
...Power terminal, 3,12...Output terminal, 4,13
...Ground terminal, CS ₁ , CS ₂ ...Constant current source, Q ₁ ,
Q ₂ , Q ₁₀ ~ Q ₁₈ ...NPN transistor, R ₁ ,
R ₂ , R ₁₀ to R ₁₄ , R _F ...resistance, C...capacitance.

Claims (1)

[Claims] 1. The base is connected to the input terminal, the emitter is connected to the second power supply, the collector is connected to the first power supply via the first resistor, and the collector is connected to the output terminal. a transistor whose anode is connected to a reference current supply circuit that supplies a reference current, a diode whose cathode is connected to the second power supply; a base which is connected to the anode of the diode, and whose collector is a third resistor; a second transistor connected to the first power supply through a second resistor, and whose emitter is connected to the second power supply through a second resistor; and a DC potential of the collector of the second transistor and the first negative feedback means to the input terminal for detecting a potential difference between the DC potential of the collector of the transistor and equalizing these DC potentials, An amplifier circuit characterized in that the current is set to be a predetermined ratio to the reference current.