JP2001094353A - Gm AMPLIFIER - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Gm amplifier where trans-conductance is never varied by temperature. SOLUTION: The Gm amplifier 1 has a voltage amplifying part 11 of an input stage, a current amplifying part 31 of the output stage, the first and second constant current circuits 51 and 61 for supplying currents I1, I2 respectively to these parts 11, 31, and ratio of the respective currents (I2/I1) has proper temperature characteristic. Since the ratio (I2/I1) of the first and second currents is constant conventionally, the trans-conductance gm is reduced with raising of the temperature. By this invention, the ratio (I2/I1) of the first and second currents is increased with raising of the temperature and a reduced portion of the trans-conductance gm can be compensated. Then, value of the trans- conductance is nearly constant though the temperature is raised.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a Gm amplifier frequently used in a filter circuit such as a band-pass filter and a high-pass filter.

[0002]

BACKGROUND ART Gm amplifier, since a wide range transconductance g _m is obtained, and the band-pass filter,
It is frequently used in filter circuits such as high-pass filters.

An example of a general Gm amplifier is shown by reference numeral 101 in FIG. 6, and its circuit block will be described below. The Gm amplifier 101 has a voltage amplifier 111 and a current amplifier 131.

The voltage amplifier 111 includes a first current supply circuit 114, a load resistor 115, and a first differential amplifier 11
6 and a load circuit 117. The first current supply circuit 114 includes two PNP transistors 118 and 11
9 and the two PNP transistors 1
A current mirror circuit is formed by 18, 18 and a diode-connected PNP transistor 152 in a first constant current circuit 151 described later.

[0005] The first differential amplifier circuit 116 has two PNPs.
It is composed of transistors 120 and 121 and each PN
The P transistors 120 and 121 are configured to be supplied with current from PNP transistors 118 and 119 in the first current supply circuit 114, respectively.

The load circuit 117 is composed of two diode-connected NPN transistors 122 and 123. The current flowing through the PNP transistors 120 and 121 in the first differential amplifier circuit 116 is applied to the load circuit 117. Are configured to flow through the NPN transistors 122 and 123 respectively.

The PN constituting the first differential amplifier circuit 116
The emitter terminals of the P transistors 120 and 121 are connected by a load resistor 115. Each of the PNP transistors 120 and 121 uses the load resistor 115 and NPN transistors 122 and 123 diode-connected as a load and is input to the base terminal. The signal is differentially amplified and output to the current amplifier 131.

The current amplifier 131 includes a second current supply circuit 132, a second differential amplifier circuit 133, first, second,
It has third current mirror circuits 134, 135 and 136.

The second current supply circuit 132 is composed of a PNP transistor.
A current mirror circuit is formed by a diode-connected PNP transistor 162 in a second constant current circuit 161 to be described later.

The second differential amplifier circuit 133 has two PNPs.
Transistors 139 and 140, each PN
The P transistors 139 and 140 are connected to the second current supply circuit 1
Current is supplied from 32. Since the second current supply circuit is composed of one PNP transistor, each PNP transistor
Transistors 139 and 140 will be supplied with current from the same PNP transistor.

The first and second current mirror circuits 134,
A current 135 is supplied to each of the PNP transistors 139 and 140 in the second differential amplifier circuit 133, and a current having the same magnitude as that of the current is supplied from the third current mirror circuit 136. Have been.

Here, the third current mirror circuit 13
The non-diode-connected transistor 138 in 6 is connected to the second current mirror circuit 135, and the connection portion is used as the output terminal 170. Therefore, the difference between the current flowing through the second current mirror circuit 135 and the current flowing through the third current mirror circuit 136 flows into or out of the output terminal 170.

Therefore, a differentially amplified signal is output from the voltage amplifying unit 111, and P
When currents of different magnitudes flow through the NP transistors 139 and 140, the difference current flows _out of the output terminal 170 as an output current Δi _out .

[0014] In Gm amplifier 101 having the above configuration, the thermal voltage _{V T (= kT / q)} ( where k is Boltzmann's constant, q is the elementary charge) and, when the output current and .DELTA.i _{o ut,} Gm The transconductance g _m of the amplifier 101 is

[0015]

(Equation 1) Indicated by

The above-described first and second constant current circuits 151,
161 is a diode-connected PNP transistor 1
52, 162 and NPN transistors 153, 163
, Constant voltage sources 154 and 164, current setting resistor 155,
165 respectively.

Each of the constant voltage sources 154 and 164 generates constant voltages V ₁ and V ₂ having no temperature dependency, and generates NPN
The voltage is applied to the base terminals of the transistors 153 and 163, respectively.

Each of the NPN transistors 153 and 163 is
The voltage V applied from each of the voltage sources 154 and 164
₁ and V ₂ , and supply currents I ₁ and I ₂ that do not have temperature dependence and correspond to the voltages V ₁ and V ₂ , respectively.

The diode-connected PNP transistors 152 and 162 have NPN transistors 15 respectively.
3, 163, the same current as the currents I ₁ , I ₂ flows.
Diode-connected PNP transistors 152, 16
2 is a PNP transistor 11 in the current supply circuit 114
8 and 119 and the current supply transistor 132, respectively, constitute a current mirror circuit, and the PNP transistors 118 and 119 and the current supply transistor 132 respectively provide the current I ₁ having no temperature dependency described above. It is configured to supply the I _2.

Conventionally, first and second constant current circuits 151,
161, the ratio of the current values of the currents I ₁ and I ₂ supplied to the current supply circuit 114 and the current supply transistor 132, respectively.
(I ₂ / I ₁ ) is configured so as to be a constant having no temperature dependence, and the term (I ₂ / I ₁ ) does not affect the temperature characteristics of the transconductance g _m. Was.

However, even with this configuration,
Since a term having a temperature dependency of (R _e1 + 2 × V _T / I ₁ ) remains in the denominator, the transconductance g _m increases or decreases according to the temperature change. Actually, the denominator term (R _e1
Due to the temperature characteristic of + 2 × V _T / I ₁ ), the transconductance g _m decreased as the temperature increased.
For this reason, when applied to a bandpass filter, there has been a problem that the center frequency of the filter fluctuates according to a temperature change.

[0022]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned disadvantages of the prior art, and has as its object to provide a Gm capable of maintaining a transconductance substantially constant regardless of a temperature change. It is to provide an amplifier.

[0023]

According to a first aspect of the present invention, there is provided a Gm amplifier including a first differential amplifier including first and second transistors for inputting a differential signal to a control terminal. An amplifier circuit, a first current supply circuit including third and fourth transistors for supplying current to the first and second transistors, respectively, are connected between the first and second transistors. A first differential amplifier stage having a load resistance, a second differential amplifier circuit including fifth and sixth transistors for inputting signals output from the first and second transistors to a control terminal, and The fifth and sixth above
A second differential amplification stage having a second current supply circuit including a seventh transistor for supplying current to the first and second transistors, and a first differential amplification stage for defining the current supplied by the first current supply circuit. A current source; a second current source for defining a current supplied by the second current supply circuit; a first current flowing through the first current source; and a second current source Has a temperature characteristic with respect to the ratio of the second current flowing through the second electrode. The invention according to claim 2 is the Gm amplifier according to claim 1, wherein the first current source is an eighth transistor, a ninth transistor, and a first current setting resistor connected in series. And a first voltage source for supplying a first voltage to the control terminal of the ninth transistor, wherein the control terminal of the eighth transistor is connected to the control terminals of the third and fourth transistors. To form a current mirror circuit. The second current source is connected to a tenth transistor, an eleventh transistor, a second current setting resistor, and a control terminal of the eleventh transistor connected in series. And a second voltage source for supplying a second voltage. The control terminal of the tenth transistor is connected to the control terminal of the seventh transistor to form a current mirror circuit. The second The ratio of the pressure has a temperature characteristic. Claim 3
The first aspect of the present invention is the Gm amplifier according to the second aspect, wherein the first voltage source includes a first constant current source and a twelfth transistor connected in series. And a second constant voltage circuit including a second constant current source and a thirteenth transistor connected in series; and an output voltage of the first constant voltage circuit, which is input to an inverting input terminal. An operational amplifier for inputting an output voltage of the constant voltage circuit to a non-inverting input terminal, a feedback resistor connected between the output terminal and the inverting input terminal of the operational amplifier, and a non-inverting input terminal of the operational amplifier A constant voltage source;
The difference between the output voltage of the constant voltage circuit and the output voltage of the second constant voltage circuit is a value corresponding to the element area ratio of the twelfth and thirteenth transistors. The invention described in claim 4 is
The Gm amplifier according to claim 1, 2 or 3, wherein
The transconductance at 75 ° C. and −25 ° C. is ± 0.2% and ± 0.1% with respect to the above-mentioned reference values, respectively, when the transconductance at 100 ° C. is a reference value.
%, The ratio between the first current and the second current is set.

In the conventional Gm amplifier, the first current and the second current
By making the ratio of the magnitudes of the currents have no temperature dependency, the transconductance did not have the temperature dependency.However, in the transconductance of the Gm amplifier, the parameter having the temperature dependency is: It is not only the ratio between the magnitudes of the first and second currents. For this reason,
Even if the ratio between the first current and the second current does not have the temperature dependency, the temperature dependency of the transconductance remains due to the influence of other parameters.

On the other hand, in the Gm amplifier of the present invention, the ratio of the magnitude of the first current to the magnitude of the second current has an appropriate temperature dependency. By preliminarily setting the parameters so as to have, even if there is a parameter having temperature dependency other than the ratio of the magnitudes of the first current and the second current, it is possible to compensate for the effect of the parameter due to a temperature change. .

For example, when the transconductance decreases as the temperature rises, the present invention makes it possible to increase the ratio of the magnitude of the second current to the magnitude of the first current as the temperature rises. By setting the increase due to temperature rise to an appropriate value, the decrease in transconductance is compensated, and even when the temperature rises, the transconductance does not decrease, and the transconductance remains almost constant. Can be kept.

In the present invention, the voltage between both terminals of the current setting resistor of the first current source (within the constant current circuit) is equal to the second voltage.
Is configured so that the temperature change rate is smaller than the voltage between both terminals of the current setting resistor of the current source (within the constant current circuit). The ratio of the current values of the two currents can be made larger as the temperature rises.

Therefore, by setting the rate of increase in the ratio of the magnitude of the first and second currents with the temperature rise to an appropriate value in advance, the decrease in the transconductance with the temperature rise is compensated for. Thus, the transconductance can be kept constant regardless of the temperature.

In the Gm amplifier of the present invention, the current source
(Constant current circuit) has a voltage source including two constant voltage circuits,
The difference between the output voltages of the two constant voltage circuits is set to a value corresponding to the emitter area ratio of the two transistors constituting each of the two constant voltage circuits.

Therefore, even if parameters in the manufacturing process vary from process to process, the emitter area ratio in each chip becomes constant, and the output voltage in each chip can be kept constant. Therefore, there is no need to make adjustments such as trimming according to variations in process parameters.

[0031]

Embodiments of the present invention will be described with reference to the drawings. Reference numeral 1 in FIG.
1 shows an m amplifier. This Gm amplifier 1 includes a voltage amplifying unit 11
, A current amplifying section 31, and first and second constant current circuits 5
1 and 61.

The voltage amplifier 11 includes a current supply circuit 14 and
It has a load resistor 15, a first differential amplifier circuit 16, and a load circuit 17. The current supply circuit 14 includes two PNs
PNP transistors 18 and 19 are provided. Each emitter terminal of each of the PNP transistors 18 and 19 is connected to the power supply voltage Vcc, and the collector terminal is connected to each other via the load resistor 15. Also, PNP transistor 1
The base terminals 8 and 19 are connected to each other.

The first differential amplifier circuit 16 has two PNPs.
Transistors 20 and 21 have their base terminals connected to the differential input terminals 12 and 13, respectively, and have their emitter terminals connected to the PNP transistor 1 of the current supply circuit 14.
8 and 19, respectively.

The load circuit 17 includes a diode-connected 2
It has NPN transistors 22 and 23, and the collector terminals of the NPN transistors 22 and 23 are connected to the collector terminals of the PNP transistors 20 and 21 of the first differential amplifier circuit 16, respectively.

The PNP transistors 18 and 19 in the current supply circuit 14 have the same area, and when a first constant current circuit 51 described later operates and becomes conductive, the first differential amplifier circuit 16 Each PNP transistor 20,
Provides a current equal to 21.

The first differential amplifier circuit 16 uses the diode-connected NPN transistors 22 and 23 in the load circuit 17 and the load resistor 15 as loads, operates with the current supplied from the current supply circuit 14, and operates as a differential input. The voltages input to the terminals 12 and 13 are differentially amplified, and the PNP transistors 20 and 21 are amplified.
Are output to the current amplifying unit 31 from the respective collector terminals.

The current amplifier 31 includes a current supply transistor 32, a second differential amplifier circuit 33, first, second, and third
Of current mirror circuits 34, 35, and 36. The current supply transistor 32 is formed of a PNP transistor, the emitter terminal of which is connected to the power supply voltage Vcc, and the collector terminal of which is connected to the second differential amplifier circuit 33.

The second differential amplifier circuit 33 has two PNPs.
It has transistors 39 and 40, each having an emitter terminal connected to the collector terminal of the current supply transistor 32 and a base terminal connected to the P terminal in the first differential amplifier circuit 16.
They are connected to the collector terminals of the NP transistors 20 and 21, respectively.

First and second current mirror circuits 34, 3
5 has NPN transistors 42 and 43 that are diode-connected, and NPN transistors 41 and 44 that are not diode-connected. Base terminals of diode-connected NPN transistors 42 and 43;
NPN transistor 41 which is not diode-connected,
The base terminals of the transistors are connected to each other, and the emitter terminals of these transistors are grounded. The collector terminals of the diode-connected NPN transistors 42 and 43 are connected to the collector terminals of the PNP transistors 39 and 40 of the second differential amplifier circuit 33, respectively.

The third current mirror circuit 36 has two PNP transistors 37 and 38, and one PNP transistor 37 is diode-connected. Each emitter terminal is connected to the power supply voltage Vcc, the base terminal is connected to each other, and the collector terminal is
It is connected to the collector terminals of the NPN transistors 41 and 44 which are not diode-connected in the first and second current mirror circuits 34 and 35, respectively. The collector terminal of the PNP transistor 38 that is not diode-connected is connected to the output terminal 70.

The current supply transistor 32 is configured to supply a current to each of the PNP transistors 39 and 40 in the second differential amplifier circuit 33 when a second constant current circuit 61 described later operates and becomes conductive. ing.

The second differential amplifier circuit 33 operates with the current supplied from the current supply transistor 32,
When a potential difference is generated between the base terminals of the PNP transistors 39 and 40 due to the differential output voltage output from 1, a current having a magnitude corresponding to the potential difference is supplied from the collector terminals of the PNP transistors 39 and 40 to the PNP transistors 39 and 40. The current is supplied to the first and second current mirror circuits 34 and 35, respectively.

First and second current mirror circuits 34, 3
5, the third current mirror circuit 3 is connected to the NPN transistors 41 and 44 which are not diode-connected.
Current is supplied from the six PNP transistors 37 and 38. Diode-connected NPN transistors 42, 4
3 flows through the collectors of the NPN transistors 41 and 44, which are not diode-connected, and supplies a current to the output terminal 70.

The above-described first and second constant current circuits 51 and 6
1 is a diode-connected PNP transistor 52,
62, NPN transistors 53 and 63, and voltage source 5
4 and 64 and resistors 55 and 65, respectively.

The emitter terminals of the diode-connected PNP transistors 52 and 62 are respectively connected to the power supply voltage Vcc, and the respective base terminals are the base terminals of the PNP transistors 18 and 19 of the current supply circuit 14 and the base of the current supply transistor 32. And the terminals.

The collector terminal of each of the NPN transistors 53 and 63 is connected to a diode-connected PNP transistor 5.
2, 62 are connected to the collector terminals, the emitter terminal is connected to the ground potential via resistors 55 and 65, respectively, and the base terminals are connected to voltage sources 54 and 64, respectively.

The NPN transistors 53 and 63 operate according to the voltages V ₁ and V ₂ applied from the voltage sources 54 and 64, respectively, and have a magnitude corresponding to the voltage applied from the voltage sources 54 and 64. The currents I ₁ and I ₂ are supplied to the diode-connected PNP transistors 52 and 62, respectively.

Each of the PNP transistors 52 and 62 diode-connected in the first and second constant current circuits 51 and 61
Constitutes a current mirror circuit between the PNP transistors 18 and 19 in the current supply circuit 14 and the current supply transistor 32, respectively, and includes PNP transistors 52 and 62, PNP transistors 18 and 19,
When the areas of the current supply transistors 32 are equal to each other, the PNP transistors 18 and 19 and the current supply transistor 32 are connected to the respective diode-connected PNs.
Currents I ₁ and I _2, which are the same as the currents flowing through P transistors 52 and 62, respectively, flow.

In the Gm amplifier 1 having the above configuration, Δm
v _i represents the potential difference between the differential input terminals 12, 13, .DELTA.i
_out indicates the output current output from the output terminal 70, and _re1 is the reciprocal (==) of the transconductance of the PNP transistors 20 and 21 in the first differential amplifier circuit 16.
V _T / I ₁₎ indicates, r _e2 is the inverse of the transconductance of the PNP transistor 39 and 40 in the second differential amplifier circuit _{33 (= V T / I 2} /2) shows the, r _e3 is Assuming that the reciprocal of transconductance of the NPN transistors 22 and 23 in the load circuit 17 (= V _T / I ₁ ), G
The transconductance g _m of m amplifier 1 is generally

(Equation 2) Indicated by

The potential difference Δv is applied to the differential input terminals 12 and 13._i
Occurs, the PNP transformer in the first differential amplifier circuit 16
The current flowing through the transistors 20, 21 changes. At this time
The current flowing through each of the PNP transistors 20 and 21 is
(I₁+ ΔI₁), (I₁-ΔI ₁), The amount of change in current
ΔI₁Is

[0051]

(Equation 3) Indicated by Here, _Re1 indicates the resistance value of the load resistor 15, and V _T = kT / q (k is Boltzmann's constant, q is the elementary charge) indicates thermal voltage.

[0052] When the potential difference between the base terminal of the PNP transistor 39 and 40 in the second differential amplifier circuit 33 in this state to Delta] v _i2, the potential difference Delta] v _i2 is

(Equation 4) Indicated by At this time, the output current Δi _out is

(Equation 5) Indicated by

When the above equation (4) is substituted into the above equation (5), the output current Δi _out becomes

(Equation 6) Indicated by By substituting the above equation (6) into the above equation (2), the transconductance g of the Gm amplifier 1 is obtained.
_m is

(Equation 7) Indicated by

In the Gm amplifier 1 having the above-described configuration, like the conventional Gm amplifier, the first and second constant current circuits 51,
Each of the voltage sources 54 and 64 in the 61 is a constant voltage source, the voltages V ₁ and V ₂ generated by the voltage sources 54 and 64 are made equal to each other, and the resistance values R ₁ and R _Two
Are equal to each other, the current values of the currents I ₁ and I ₂ supplied to the current supply circuit 14 and the current supply transistor 32 become equal to each other, and (I ₂ / I ₁ ) on the right side of the above equation (7) Is a constant that does not depend on the temperature of 1, so (I ₂ / I
Effect of the temperature characteristic by claim ₁₎ does not extend to the transconductance g _m.

However, even with this configuration,
Since the term (R _e1 + 2 × V _T / I ₁ ) has a temperature dependency, the transconductance g _m has a temperature dependency. Indeed the extent transconductance g or decrease of _m is described below.

Table 1 shows that the Gm amplifier 1 supplies current.
Current supplied to the circuit 14 and the current supply transistor 32
I₁, I_TwoWhen the current values of
Current setting resistors 55 and 6 at temperatures of 50 ° C. and 75 ° C.
5 voltage V between both terminals_R1, V _R2And each current setting resistor 5
Resistance value R of 5, 65₁, R_TwoAnd the resistance value R of the load resistor 15
_e1And thermal voltage V_TAnd the first and second constant currents
The current I supplied from the circuits 51 and 61₁, I_TwoCurrent value
And the temperature coefficient P of each value₁, M_Two, M_Three, P_FourAnd warm
Each value in the degree change amount ΔT is shown. In addition, temperature
The change amount ΔT is the temperature change amount based on 25 ° C.
At 75 ° C., ΔT = 50 ° C.

[0057]

[Table 1] By substituting each value of Table 1 into the above equation (7), the transconductance g _m of the Gm amplifier 1 at the temperature change ΔT is

[0058]

(Equation 8) Indicated by

From the above equation (8), in the Gm amplifier 1 in which the current values of the currents I ₁ and I ₂ supplied to the current supply circuit 14 and the current supply transistor 32 are equal, the transconductance at 25 ° C. (ΔT = 0 ° C.) g _m (at 25 ° C) and 75 ° C (Δ
T = 50 ° C.) transconductance g _m (at 75
° C) are (4.52 × 10 ⁴ ) ^-1 (Ω ^-1 ) and (3.
6646 × 10 ⁴ ) ^-1 (Ω ^-1 ) and 75 ° C. (ΔT = 50
C) is the transconductance g _m (at 75 ° C)
Transconductance g _m at 25 ° C. (ΔT = 0 ° C.) (at 2
(5 ° C.), which indicates that the transconductance g _m greatly changes due to a temperature change.

Therefore, in the Gm amplifier 1 of the present embodiment,
In order to maintain the transconductance g _m at a constant value irrespective of the temperature, the first and second constant current circuits 51, 61
The voltages V _k generated by the second voltage sources 54 and 64, respectively,
Of the voltage value of V _2, the voltage V ₂ in which the second voltage source 64 generates is as well as to have no prior similar temperature characteristics, voltage V _k of the first voltage source 54 generates in response to the temperature The first and second constant current circuits 51 and 61 are adapted to control the current I ₁ and I ₂ respectively supplied to the current supply circuit 14 and the current supply transistor 32 so as to have a temperature dependency. ing.

First, what temperature characteristics the voltage Vk should have in order for the transconductance g _m to take a constant value will be described, and the specific configuration of the voltage source 54 will be described in detail. Will be described later. Voltage source 54
Generates a constant voltage, the voltage V _R1 between both terminals of the current setting resistor 55 in the first constant current circuit 51 is
A value different from the voltage V _R2 between both terminals of the current setting resistor 65 in the second constant current circuit 61, that is,

It is assumed that V _R1 = 0.5 (1 + P ₀ × ΔT). Here, P ₀ is a temperature coefficient of the voltage V _R1 between both terminals of the current setting resistor 55 in the first constant current circuit 51. The transconductance g _m of the Gm amplifier 1 having such a configuration.
Is similar to equation (8) above.

[0063]

(Equation 9) Indicated by In the above equation (9), (1 + P ₀ × ΔT) is expressed as x
And As described above, the values of P ₁ , M ₂ , M ₃ , and P ₄ are respectively +4000 PPM, −3200 PPM, −3800 PPM,
+3331 PPM, ΔT = 50 ° C., (1 + P
₁ × ΔT) = 1.2, and (1 + P ₄ × ΔT) = 1.16
655, (1 + M ₂ × ΔT) = 0.84, and (1
+ M ₃ × ΔT) = 0.81.

By substituting these values into the above equation (9), ΔT
= The transconductance g _m (at 75 ° C) of Gm amplifier 1 at 50 ° C or 75 ° C is

(Equation 10) Indicated by

Similarly, at ΔT = 0 ° C., that is, at 25 ° C., the transconductance g _m (at 2
5 ° C)

[Equation 11] Indicated by

At 25 ° C. and 75 ° C., in order for the transconductance g _{m to} have the same value and be constant within the range of 25 ° C. to 75 ° C., g _m (at 25 ° C.) = G _m (at
75 ° C.), so that the above equation (10) and the above equation (11) should be equal. X at this time is x = 1.516
8, that is, P ₀ = + 1034 PPM.

The current setting resistor 5 in the first constant current circuit 51
Voltage V _R1 applied to both ends of the _{5, 0.5 (1 + P 0 ×} Δ
T 0) and as described above, P ₀ = + 1034 PPM
Therefore, at ΔT = 0 ° C., the voltage V _R1 is 0.5 (1 + 0.01
034 × 0) = 0.5 (V), while ΔT = 50 ° C.
And the voltage V _R1 is 0.5 (1 + 0.01034 × 50) = 0.
7584 (V).

The voltage V _k applied to the base of the current setting transistor 53 is a value obtained by adding the above-mentioned voltage V _R1 and the base-emitter voltage V _BE of the current setting transistor 53 to the base-emitter voltage. V _BE is 25 ° C, 7
It becomes 0.7 (V) and 0.6 (V) at 5 ° C., respectively.
At T = 0 ° C., the voltage V _k becomes 0.7 + 0.5 = 1.2 (V), and at ΔT = 50 ° C., the voltage V _k becomes 0.6 + 0.7584 =
1.3584 (V).

As described above, in order for the transconductance g _m of the Gm amplifier 1 to take a constant value in the range of 25 ° C. to 75 ° C., the base of the current setting transistor 53 in the first constant current circuit 51 is required. The voltage V _k applied to the terminal is 1.2 (V) at ΔT = 0 ° C. and 50 ° C., respectively.
It suffices to have a voltage characteristic of 1.3584 (V).

FIG. 2 shows a detailed configuration of the voltage source 54 having such voltage characteristics. The voltage source 54 includes a voltage setting unit 90
And a constant voltage source 82. The voltage setting unit 90
It has two constant voltage circuits 83 and 84 and an amplifier unit 85.

The constant voltage circuits 83 and 84 are connected to the constant current circuit 7
1 and 72, and one diode-connected NPN transistor 73 and 74, respectively. One end of each of the constant current circuits 71 and 72 is connected to the power supply voltage Vcc, and the other end is connected to the collector terminal of each of the NPN transistors 73 and 74.
The emitter terminals 3 and 74 are both connected to the ground potential.

Each of the constant current circuits 71 and 72 supplies a constant current I _{3 of the} same magnitude to each of the NPN transistors 73 and 74.
When the constant current I ₃ flows through each of the NPN transistors 73 and 74, predetermined voltages V ₃ and V ₄ are generated at the respective collector terminals and output to the amplifier unit 85. I have.

The amplifier section 85 has an operational amplifier 79, input buffers 75 and 76, input resistors 77 and 78, a negative feedback resistor 80, and a resistor 81. Input resistance 77,
The resistance value of 78 is set to the same resistance value R ₃ ,
The negative feedback resistor 80 and the resistor 81 have the same resistance value R
Set to ₄ .

Input buffers 75 and 76 are connected to the inverting input terminal and the non-inverting input terminal of the operational amplifier 79 via input resistors 77 and 78, respectively. The input buffers 75 and 76 are connected to constant current circuits 83 and 84, respectively. Connected to each other.

The output terminal of the operational amplifier 79 is connected to the base terminal of the current setting transistor 53 in the first constant current circuit 51, and a negative feedback resistor 80 is connected between the output terminal and the inverting input terminal. In addition, one end of a constant voltage source 82 is connected to the non-inverting input terminal via a resistor 81, and the other end of the constant voltage source 82 is grounded.

Voltages V ₃ and V output from NPN transistors 73 and 74 in constant voltage circuits 83 and 84, respectively.
₄ is input to an inverting input terminal and a non-inverting input terminal of an operational amplifier 79 via input buffers 75 and 76 and input resistors 77 and 78, respectively.

The non-inverting input terminal of the operational amplifier 79 receives the predetermined voltage _VA output from the constant voltage source 82 and having no temperature characteristics via the resistor 81, and receives the predetermined voltages V ₃ and V ₃ described above. ₄ difference (V ₄ -V _3), the ratio of the resistance value R ₃ of the input resistor 77 and the resistance value R ₄ of the negative feedback resistor 80 (R ₄ / R ₃₎ is amplified doubled, the constant voltage to the amplified voltage The voltage V _k added to the voltage _VA generated by the source 82, that is,

(Equation 12) Is output from the output terminal of the operational amplifier 79 to the base terminal of the current setting transistor 53 in the first constant current circuit 51.

The above-mentioned predetermined voltages V ₃ and V ₄ are represented by V _T ln (I ₃ / I _s3 ) and V _T ln (I ₃ / I _{s 4} ), respectively (where I _s3 and I _s4 are (Emitter area of each NPN transistor 73, 74). The area ratio of the NPN transistors 73 and 74 N: 1 and then, the area of one of the NPN transistor 74 when the I _s, since the area of the other NPN transistor 73 becomes NI _s, predetermined voltage V _3, V ₄ Potential difference (V ₄ −
V ₃ )

(Equation 13) Indicated by

From the above equation (13), the potential difference (V ₄ −V ₃ ) is N
The natural logarithm of the area ratio N of the PN transistors 73 and 74;
Represented by the product of the thermal voltage V _T. Even if process parameters vary from one process to another, the area ratio is constant for each chip, so that the potential difference (V ₄ −V ₃ ) shows a constant value between each chip.

By substituting the above equation (13) into the above equation (12),
The voltage V _k is

[Equation 14] It is represented by

As described above, in order for the transconductance g _m to be constant irrespective of the temperature, 75 ° C. (ΔT =
V _k (at 75 ° C.) of 1.3584 (V) at 25 ° C.
Since V _k (at 25 ° C.) at (ΔT = 0 ° C.) is 1.2 (V), in this case, V _k (at 75 ° C.) and V _k (at 25 ° C.)

(Equation 15) When,

(Equation 16) And is indicated by Here, NPN transistors 73 and 74
Is set to N = 10.

By subtracting the above equation (16) from the above equation (15),

[Equation 17] Get. From the above Table 1, V _T (at 75 ° C.) is 34.67 (mV).
V _T (at 25 ° C.) is 26 (mV). These values are
By substituting into (17),

[0083]

(Equation 18) Get. When the above equation (18) is substituted into the above equation (15),

[Equation 19] Therefore, the voltage value _VA of the constant voltage source 82 is

_VA = 1.2−V _T (at 25 ° C.) × ln10 = 1.2−15.89 × 26 × 10 ⁻³ × ln10 = 0.249 (V)

As described above, by setting (R ₄ / R ₃ ) and V _A to 15.84 and 0.249 (V), respectively,
The above-described voltage source 54 can output a voltage V _k of 1.2 (V) at 25 ° C. and 1.3584 (V) at 75 ° C.
In a temperature range of 5 ° C. or more and 75 ° C. or less, the transconductance g _m of the Gm amplifier 1 can have a constant value.

In the voltage source 54 having the above configuration, the voltage setting section 9
0, the area ratio N and the resistance ratio (R_Four/ R _Three), Thermal volte
Page V_TAlone determines the temperature characteristics and the manufacturing process conditions
Need to be adjusted by trimming etc.
Absent.

The present inventors have determined that the transconductance g of each of the Gm amplifier 1 of the present embodiment having the voltage source 54 and the conventional Gm amplifier 101 is different.
_m1 and _gm101 were actually measured. The measurement results are shown in Table 2 below.

[0088]

[Table 2]

According to Table 2 above, the transconductance g _m1 of the conventional Gm amplifier 1 fluctuates by about 23.9% in the temperature range of −25 ° C. to 75 ° C. The transconductance g _m1 of
Only not fluctuate about 0.29% at the same temperature range, it can be seen that the variation of transconductance g _m is very small compared with the conventional.

Further, the inventors of the present invention simulated the operation of each of the bandpass filter using the Gm amplifier 1 having the above-described configuration and the bandpass filter using the conventional Gm amplifier 101.

The band pass filter used in the operation simulation is indicated by reference numeral 91 in FIG. The band-pass filter 91, first, and second Gm amplifier ₁ 1, 1 _2, and one of the constant voltage source 92, first and second capacitors 93 and 94
And

[0092] negative terminal of the constant voltage source 92 is connected to the ground potential, the positive terminal is connected to the first non-inverting input terminal of the Gm amplifier 1 _1. The first output terminal of the Gm amplifier 1 ₁ is connected to a second non-inverting input terminal of the Gm amplifier 1 _2, the output terminal of the second Gm amplifier 1 ₂ is connected to one end of the first capacitor 93 And the first capacitor 9
The other end of 3 is connected to the ground potential. First, second Gm amplifier ₁ 1, 1 ₂ of the inverting input terminal are connected to each other,
It is connected to a second output terminal of the Gm amplifier 1 _2.

The output terminal of the _first Gm amplifier 11 is connected to a signal source 95 via a second capacitor 94.
When a signal is input from the signal source 95, the signal is passed only through a specific frequency band centered on the center frequency f ₀ and output from the output terminal of the _second Gm amplifier 12.

The band-pass filter 91 having such a configuration will be described.
And its center frequency f₀₁And the conventional Gm
Regarding the bandpass filter using the amplifier 101,
Center frequency f₀₁₀₁I asked. The band so determined
Center frequency f of pass filter ₀₁, F₀₁₀₁In Table 3 below
Show.

[0095]

[Table 3]

From Table 3 above, it can be seen that the conventional Gm amplifier 101
The center frequency f ₀₁₀₁ of the bandpass filter using
In contrast to the variation of about 2.6%, the Gm
For the band pass filter using the amplifier 1 _1, 1 _2, -
In the temperature range of 25 ° C. to 75 ° C., the center frequencies f ₀₁ are all 218.8 (kHz), indicating that there was no change at all.

The waveform diagram of the frequency characteristic of the band-pass filter using the conventional Gm amplifier 101 is shown by a curve (A) in FIG.
(B) and (C) show. These curves (A), (B), (C)
Waveform diagrams at temperatures of −25 ° C., 25 ° C., and 75 ° C. are shown. From these curves (A), (B) and (C),
It can be seen that the frequency characteristic changes depending on the temperature.

On the other hand, curves (D), (E), and (F) of FIG. 5 show waveform diagrams of the frequency characteristics of the band-pass filter when the Gm amplifier of this embodiment is used. These curves (D), (E), and (F) show that the temperatures are −25 ° C., 25 ° C., 75 ° C.
Waveform diagrams in the case of ° C are shown. Curve (D),
(E) and (F) almost coincide with each other, and it can be seen that the frequency characteristics are hardly affected by the temperature.

Further, when manufacturing the above-described voltage source 54, the NPN transistors 73 and 74 in the voltage setting unit 90 are used.
Is a variation from the reference value emitter areas I _s, and if the emitter area I _s is (reference value + 30%), (reference value -30%)
Each Gm amplifier case, the respective center frequencies f ₀₁ when provided in the band-pass filter described above, it was determined by simulation. The results are shown in Table 4 below.

[0100]

[Table 4]

[0102] From Table 4 above, and if the emitter area I _s was used Gm amplifier (reference value + 30%), (reference value -
30%), the center frequency f ₀₁ is 218.8 (kHz) at -25 ° C., 25 ° C., and 75 ° C., and does not vary with temperature. in the case where the emitter area I _s varies by the process it is also quite apparent that the variation is not found in the center frequency f _01.

In the present embodiment, the voltage V ₁ generated by the voltage source 54 in the first constant current circuit 51 is made variable, and the voltage V ₂ generated by the voltage source 64 in the second constant current circuit 61 is changed.
Although being a constant value, the present invention is not limited to this, the voltage V ₂ second constant current circuit 52 is generated can be controlled, the voltages V ₁ to a constant value by the first constant current circuit 51 generates May be configured. Furthermore, a configuration may be adopted in which both the voltage values V ₁ and V ₂ of the voltages generated by the voltage sources 54 and 64 in the first and second constant current circuits 51 and 52 can be controlled. Further, as the configuration of the voltage source 54, a circuit as shown in FIG. 3 has been described.
Is not limited to this.

[0103]

The transconductance can be made independent of temperature changes.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a Gm amplifier according to the present invention.

FIG. 2 is a circuit diagram showing an example of a voltage source of the Gm amplifier of the present invention.

FIG. 3 is a circuit diagram illustrating a configuration of a bandpass filter used for an operation simulation of the Gm amplifier according to the present invention.

FIG. 4 is a graph for explaining an operation simulation result of a conventional Gm amplifier.

FIG. 5 is a graph for explaining the operation simulation result of the Gm amplifier according to the present invention.

FIG. 6 is a circuit diagram showing an example of a conventional Gm amplifier.

[Explanation of symbols]

1 Gm amplifier 11 Voltage amplifier (first amplifier circuit) 16 First differential amplifier circuit (differential amplifier circuit)
15 Load resistors 22, 23 NPN transistors (transistors) 31 Current amplifiers (second amplifier circuits) 51 First constant current circuits 54, 64 Voltage sources 55, 65 Current settings Resistance 61: second constant current circuit

Continued on the front page F term (reference) 5J066 AA01 AA12 AA17 AA43 AA45 AA59 CA02 CA81 CA84 FA08 FA10 FA16 HA07 HA08 HA25 HA29 KA02 KA03 KA06 KA09 KA12 KA41 KA47 MA08 MA21 MD05 ND05 ND07 ND23 ND25 PD01 SA01 TA01 A01 TA01 AA45 AA59 CA02 CA81 CA84 CN02 FA08 FA10 FA16 FN01 FN06 HA07 HA08 HA25 HA29 HN16 KA02 KA03 KA06 KA09 KA12 KA41 KA47 MA08 MA21 SA13 TA01 TA03 TA04 5J091 AA01 AA12 AA17 AA43 AA45 HA08 HA03 HA08 CA08 CA08 KA12 KA41 KA47 MA08 MA21 SA13 TA01 TA03 TA04

Claims (4)

[Claims] 1. A first differential amplifier circuit including first and second transistors for inputting a differential signal to a control terminal, and third and fourth transistors for supplying current to the first and second transistors, respectively. A first current supply circuit including four transistors, a first differential amplifier stage having a load resistor connected between the first and second transistors, and the first and second transistors. Differential amplifier circuit including fifth and sixth transistors for inputting a signal output from the control terminal to a control terminal, and a second differential amplifier circuit including a seventh transistor for supplying current to the fifth and sixth transistors. A second differential amplifier stage having a current supply circuit, a first current source for defining a current supplied by the first current supply circuit, and a current supplied by the second current supply circuit A second current source for defining The a, Gm amplifier having a specific temperature characteristic of a second current flowing through the first current and the second current source flowing through the first current source. 2. The first current source includes an eighth transistor, a ninth transistor, a first current setting resistor connected in series, and a first voltage applied to a control terminal of the ninth transistor. And a control terminal of the eighth transistor is connected to control terminals of the third and fourth transistors to form a current mirror circuit. A tenth transistor, an eleventh transistor, a second current setting resistor, and a second voltage source for supplying a second voltage to a control terminal of the eleventh transistor, which are connected in series, The control terminal of the tenth transistor is connected to the control terminal of the seventh transistor to form a current mirror circuit, and a ratio between the first voltage and the second voltage has a temperature characteristic. G described in Amplifier. 3. The first constant voltage source includes a first constant current source and a twelfth transistor connected in series, and a second constant current source connected in series. And a second constant voltage circuit including a third transistor and an output voltage of the first constant voltage circuit to an inverting input terminal.
An operational amplifier for inputting the output voltage of the constant voltage circuit to the non-inverting input terminal, a feedback resistor connected between the output terminal and the inverting input terminal of the operational amplifier, and a non-inverting input terminal of the operational amplifier. A constant voltage source, wherein the difference between the output voltage of the first constant voltage circuit and the output voltage of the second constant voltage circuit is a value corresponding to the element area ratio of the twelfth and thirteenth transistors. The Gm according to claim 2, which is
Amplifier. 4. When the transconductance at 25 ° C. is set as a reference value, the transconductance at 75 ° C. and at −25 ° C. is ±.
0.2%, ± 0.1% within the above range.
4. The Gm amplifier according to claim 1, wherein a ratio between the current and the second current is set.