JP2906414B2 - Voltage-current conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of converting an input voltage into a current and outputting the current.
The present invention relates to a current conversion circuit, and more particularly, to a voltage-current conversion circuit also called a Gm circuit using a transistor differential pair.

[Summary of the Invention]

The present invention provides a voltage-current conversion circuit that converts an input voltage to a transistor differential pair into a current and outputs the current, wherein the first current source connected to the first power supply terminal and the second current supply terminal are connected to the second power supply terminal. By inserting a plurality of diodes, which are turned on by the second current source, between the emitters of the transistor differential pair, low-voltage operation can be performed while securing a large dynamic range. .

[Conventional technology]

A voltage-current conversion circuit known as a so-called Gm circuit basically has a configuration as shown in FIG.

In FIG. 5, an input voltage v _i (variation) is supplied between base input terminals of a differential amplifier composed of a pair of transistors 11 and 12 whose emitters are connected in common. The output current i _o (change) is extracted from the terminal. The common emitter connected to a ground terminal 13 serving as a first power supply terminal through the constant current source 2I _0, the collectors of transistors 11 and 12 is connected to the V _cc power supply terminal 14 as a second power supply terminal and also the reference bias voltage V _r to the input voltage v _i is superimposed.

Voltage, such as the Figure 5 - the current conversion circuit (Gm circuit), when the relationship between the output current i _o with respect to the input voltage v _i, expressed as _{i o = v i × Gm,} Gm = 1 / 2r e However, r _e is the operating resistance of transistors 11 and 12, and r _e =
V _T / I ₀ ≡kT / qI ₀ Input dynamic range in the Gm circuit having such a configuration, since narrow and ± V _T, for example, resistors to the emitters of the transistors 11 and 12 as shown in FIG. 6
The dynamic range can be increased by inserting and connecting R _E and R _E , or by inserting and connecting diodes (transistor-connected diodes) 15 and 16 to the emitters of the transistors 11 and 12 as shown in FIG. Spreading. Gm circuit of the sixth view in this case, Gm = 1/2 (R E + r e) , and the addition Gm circuit of FIG. 7 is a Gm = 1 / 4r _e.

However, when an active filter is formed using such a Gm circuit, it is preferable in terms of characteristics to use the circuit shown in FIG.

That is, FIG. 8 shows a low-pass filter formed using the Gm circuit of FIG. 7, and a constant current source serving as a load between the collector of one transistor 12 of the differential pair and the _Vcc power supply terminal 13. The AC output current i _o is taken out by inserting and connecting the 17. A capacitor C is connected between the collector output terminal and the ground terminal 14, and the output of the capacitor C is taken out via the transistor 18. A constant current load 19 is connected to the emitter of the transistor 18, and the emitter output is fed back to the base of the transistor 12. When the emitter output voltage of the output transistor 18 of the Figure 8 and _{v o, (v i -v o} ) × Gm × (1 / sC) = v o v i -v o = v o sC / Gm v i _{/ v o = 1 / (1} + sC / Gm) ... here, Gm = 1 / 4r _e, thus _{r e = V T / I 0} , the cut-off frequency f _c of the lowpass filter structure shown in FIG. 8, equation Thus, f _c = 1 / (2πC / Gm). For example by reducing the Gm in order to lower the cut-off frequency f _c.

Low-pass filter structure shown in FIG. 8 is, Gm is proportional to the current I _0, because it does not depend on the internal resistance, it is possible to change the cut-off frequency f _c of the filter by varying the current I _0. Also the constant current I _0, the temperature characteristic by using an external resistor R _out of approximately 0, by setting as _{I 0 = V T / R out} , r e = V T / I 0 = R _out next, it can be substantially zero temperature characteristics of r _e, even if the temperature characteristics of the cut-off frequency f _c can be reduced to substantially zero.

In contrast, when a low-pass filter by using the circuit of FIG. 6 will become the Gm depends on the resistance R _E, also it would not be avoid the influence of temperature characteristics.

[Problems to be solved by the invention]

By the way, in the Gm circuit (voltage-current conversion circuit) as described above, if the dynamic range is to be further expanded, as shown in FIG.
It is necessary to insert and connect a plurality (for example, N-1) of diodes (for example, a diode-connected transistor) 15 and 16 to each emitter side of 1 and 12 in series. That is, Gm of the circuit of FIG.
Is, Gm = 1 / 2Nr _e becomes, the higher the input dynamic range number of N increases so take widely. For example, the dashed line in FIG. 10 shows an input-output characteristic curve when the above-mentioned diode is not inserted and connected, and the solid line shows a case where N-1 (N is an integer of 2 or more) diodes 15 and 16 are inserted and connected, respectively. input - shows the output characteristic curve, thus the number of insertion diode becomes small slope enough characteristic curve increases change as a linear region increases, the input dynamic range for example D ₁ D _N It is expanded to. However, the common connection terminals of the diodes 15 and 16 and the constant current source 2I
The voltage V _E at the connection point with _o is V _E = V _r −NV _BE , and the reference bias voltage V _r needs to be set higher than the NV _BE , and the power supply voltage V _cc is higher. Voltage will be required.

In particular, in recent years, various small-sized electronic devices using a dry battery have become widespread, and from this viewpoint, it is strongly desired to realize a wide dynamic range with a low-voltage power supply.

The present invention has been made in view of such circumstances, and has as its object to provide a Gm circuit or a voltage-current conversion circuit capable of expanding a dynamic range without increasing a power supply voltage.

[Means for solving the problem]

In order to solve the above-described problem, the voltage-current conversion circuit according to the present invention converts a voltage supplied between input terminals of a transistor differential pair composed of a pair of transistors of the same type to a voltage applied to each of the transistor differential pairs. A voltage-current conversion circuit for converting current from the output terminal of one of the transistors into a current and extracting the current, at least two first current sources having one ends connected to the first power supply terminal, and one end connected to the second power supply terminal. And at least one second current source having one end connected to the other end of the first current source and the other end connected to the other end of the second current source. A plurality of diode groups each including a diode, wherein the diode group is inserted between the emitters of the transistor differential pair and is turned on by the first and second current sources. To It is a symptom.

(Operation)

Any number of diodes turned on by the first current source and the second current source can be inserted and connected between the emitters of the transistor differential pair without increasing the power supply voltage. Therefore, a large dynamic range can be realized even at a low power supply voltage.

〔Example〕

FIG. 1 is a block diagram showing a first embodiment as a basic configuration of a voltage-current conversion circuit according to the present invention.

In a first embodiment shown in FIG. 1, between each base input terminal of the pair of transistors 11 and 12 constituting the differential pair of transistors, the input voltage (variation) v _i are supplied, One transistor 12 of the transistor differential pair
From the collector output terminal an output current (change amount) i ₀ is adapted to be taken out. Further, one ends of the first ground terminal 13 to the two first which is a power supply terminal of the current sources 31 and 32 are connected, one second to V _cc power supply terminal 14 as a second power supply terminal is connected to one end of a current source 41, each of these current sources 31, 32 is a constant current source of a current value 2I ₀ none.
Note the reference bias voltage V _r is superimposed on the input voltage v _i.

Diodes (diode-connected transistors) 21, 22 are inserted and connected in series between the emitters of the transistors 11, 12, and these diodes 21, 22 are connected to the first and second current sources 31, 32, respectively. , 41 so as to be turned on. That is, the anodes of the diodes 21 and 22 are commonly connected to the other end of the second current source 41,
The cathodes of the diodes 21 and 22 are connected to the other ends of the first current sources 31 and 32, respectively.
The emitters 1 and 12 are connected to the other ends of the first current sources 31 and 32, respectively. Therefore, the circuit configuration is bilaterally symmetrical about the second current source 41.

In the first embodiment, two diodes are provided between the emitters of the transistors 11 and 12 forming a differential pair.
Since 21 and 22 are inserted in series, the AC similar to the Gm circuit of Figure 7 described above, and has a Gm = 1 / 4r _e. On the other hand, the DC potential V _{K1 at} the connection point between the emitter of the transistor 11 and the current source 31 and the DC potential V _{K2 at} the connection point between the emitter of the transistor 12 and the current source 32 are V _K1 = V _K2 = V _r -V _bE next, it can be seen that can afford the V _bE component to the power supply as compared to the example of FIG. 7. Note DC potentials V _A at the connection point between the anode and the current source 41 of the diode 21 and 22 is equal to the V _r.

According to the circuit configuration shown in FIG. 1, it is possible to provide a voltage-current conversion circuit having a wide input dynamic range and capable of operating at a low voltage.

Here, a configuration using a first current source connected to the first power supply terminal and a second current source connected to the second power supply terminal in relation to the common emitter of the transistor differential pair is a special feature. Japanese Patent Publication No. 57-39683 discloses a technique for changing a quiescent current set value of a differential pair transistor in accordance with an input signal. Is also different from the present invention.

Next, in the second embodiment shown in FIG. 2, the other end of the second current source 41 (that is, the terminal opposite to the one end connected to the second power supply terminal 14) is connected to the first current source 41. 2 between the other end of 31 (a terminal opposite to one end connected to the first power supply terminal 13).
Diodes 21a and 21b are connected in series, and two diodes 22a are connected between the other end of the second current source 41 and the other end of the first current source 32. , 22b are inserted and connected in series. These diodes 21a, 21b, 22a, 22b are connected to the respective current sources 31, 32, 41
The direction of each anode and cathode is determined so as to be in the ON state, and they are configured symmetrically with respect to the second current source 41. The circuit of the second embodiment includes a pair of differential transistors 11, 12 and four diodes 21a, 21b, 22.
a, since six r _e is to be connected in series with the 22b,
Gm of the circuit is Gm = 1 / 6r _e , and the voltages V _K1 , V _{K1 at} the other ends of the first current sources 13 and 32 are respectively described.
_K2 and the voltage V _A of the other end of the second current source 41, a _{V K1 = V K2 = V r} -V BE V A = V r + V BE. Therefore, a wide input dynamic range can be ensured even when the power supply voltage is low.

Next, FIG. 3 shows a third embodiment, in which four pairs of two transistors (a total of 8 pairs) are provided between the emitters of the transistors 11 and 12 of the differential pair.
) Diodes (diode-connected transistors) 21a to 24b are connected in series, and these diodes 21a to 24b are connected to the first current sources 31, 32, 33 and the second current source.
The first current source 32 is symmetrical with respect to the left and right so that both are turned on by 41 and 42. That is, the diodes 21a and 21b are connected so that a current flows from the second current source 41 toward the first current source 31, and the current sources
Diodes 22a and 22b are connected from 41 to the current source 32, and diodes 23a and 22b are connected from the current source 42 to the current source 32.
3b are connected, and diodes 24a and 24b are connected from the current source 42 to the current source 33. Gm of the circuit is Gm = 1 / 10r _e, the voltage V _K1, V _K2 for each of the other ends of the current source 31, 32, 33, V
The voltages V _A1 and V _{A2 at the} other end of _{K 3} and the current sources 41 and 42 are V _K1 = V _K2 = V _K3 = V _r -V _BE V _A1 = V _A2 = V _r + V _BE . Therefore, a wide dynamic range can be realized without having to increase the power supply voltage.

An example of such a general configuration of the voltage-current conversion circuit according to the present invention is shown in FIG. 4 as a fourth embodiment. In the fourth embodiment, n terminals (n is an integer of 2 or more) each having one end connected to a ground terminal (first power supply terminal) 13 are provided.
A first current source 3 ₁ to 3 _n of the one end V _cc power supply terminal (second power supply terminal) 14 respectively connected to the n-1 of the second current source 4 ₁ to 4 _n-1 and the 1 illustrates a voltage-to-current conversion circuit using.

In FIG. 4, J-1 diodes (diode-connected transistors) are connected in series between the emitter of one transistor 11 of the transistor differential pair and the other end of the _first current source 31. Symmetrically connected to the emitter of the other transistor 12 of the differential pair and the first current source 3 _n
J-1 diodes are inserted and connected in series between the other end of the diode. Further, the K-number of the diode between the second current source 4 ₁ of the other end and the first current source 3 ₁ of the other end inserted and connected in series, a second current source to the symmetrical 4 _n- It is inserted and connected the K diode in series between the _first other end with the other end of the first current source 3 _n. Hereinafter Similarly, the second current source 4 ₁ and the first current source
3 ₂ inserted and connected the L diode in series between and between this and the second current source in a symmetrical 4 _n-1 and the first current source 3 _n-1, a second current source 4 ₂ and insert the M diode in series between and between the second current source 4 _n-2 and the first current source 3 _n-1 to the symmetry of the first current source 3 ₂ connection,…
Then, a total of 2n sets of diode series circuits are inserted and connected in series between the emitters of the differential pair transistors 11 and 12. Here, if the above n is an even number, n−
A current source 4 at a central position among _one second current sources 41 to 4 _n-1
The circuit configuration is bilaterally symmetrical with respect to _{n / 2} , and if n is an odd number, n first current sources as in FIG.
3 ₁ to 3 _n current source 3 in the central position of the _{(n + 1) / 2} becomes the circuit configuration of the symmetrical about the.

Here, if the circuit configuration is bilaterally symmetric, any natural number or 0 can be selected as J, K, L, M,. However, in order to keep the power supply voltage low, it is better not to make the number too large. Moreover, pair ratio of the current source due to the offset voltage line symmetry relation (the ratio of the current source 3 ₁ and 3 _n, 3 ₂ and 3 _n-1 and a ratio of 4 ₁ and 4 ratios, etc. of the _n-1) is It gets worse if it is off. Other deterioration of the pair ratio does not result in deterioration of the offset voltage, but results in deterioration of the dynamic range.

By adopting the circuit configuration as shown in FIG. 4, it is possible to greatly expand the input dynamic range without extremely increasing the power supply voltage. Note that the present invention is not limited to the above embodiment, and a resistor may be inserted in series between each emitter of the transistors 11 and 12 of the differential pair in addition to the diode.

〔The invention's effect〕

According to the current-voltage conversion circuit of the present invention, at least one end of which is connected to the first current source and the other end of which is connected to the second current source, between the emitters of the transistor differential pair including the pair of transistors of the same type. By inserting and connecting a plurality of diode groups each including one diode, the number of diodes inserted in series between the emitters of the transistor differential pair is increased without increasing the power supply voltage, thereby reducing the Gm of the circuit. Since the input dynamic range can be expanded, a large input dynamic range can be realized even at a low power supply voltage. Also, by connecting the emitter of the transistor differential pair directly to the first current source, the dynamic range can be increased and the power consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a voltage-current conversion circuit according to the present invention, FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and FIG. Circuit diagram showing an embodiment of
FIG. 4 is a circuit diagram showing a fourth embodiment of the present invention, FIG. 5 is a circuit diagram showing a basic configuration of a conventional voltage-current conversion circuit (Gm circuit), and FIG. 6 is another conventional example. 7 is a circuit diagram showing still another conventional example, FIG. 8 is a circuit diagram showing a low-pass filter using the circuit (Gm circuit) of FIG. 7, and FIG. 9 is an input dynamic range. And FIG. 10 is a characteristic diagram showing an input voltage-output current characteristic. 11, 12: transistors of a differential pair 13: first power supply terminal (ground terminal) 14: second power supply terminal ( _Vcc power supply terminal) 15, 16, 21, 22, 21a to 24b: diode 31,32,33,3 ₁ ~3 _n ...... first current source 41,42,4 ₁ ~4 _n-1 ...... second current source

Claims (2)

(57) [Claims] 1. A voltage-current converter for converting a voltage supplied between input terminals of a transistor differential pair composed of a pair of transistors of the same type into a current from an output terminal of one transistor of the transistor differential pair and extracting the current. In the conversion circuit, at least two first current sources each having one end connected to the first power supply terminal; at least one second current source having one end connected to the second power supply terminal; At least one of which one end is connected to the other end of the first current source and the other end is connected to the other end of the second current source
A plurality of diode groups each including a plurality of diodes, wherein the diode group is inserted and connected between emitters of the transistor differential pair, and is turned on by the first and second current sources. Characteristic voltage-current conversion circuit. 2. The voltage generator according to claim 1, wherein said emitter is directly connected to said first current source.
Current conversion circuit.