JP2911131B2 - Integrated circuit - Google Patents

Description

The present invention relates to an integrated circuit having a plurality of built-in amplifier circuits.
In particular, the present invention relates to an integrated circuit that can be easily miniaturized and can improve characteristics and is suitable for driving a headphone or the like.

(B) Prior art Japanese Patent Application No. 63-219214 discloses an integrated circuit as shown in FIG.

In FIG. 2, (1) is a first amplifier circuit for amplifying a small signal, (2) and (3) are first and second resistors for negative feedback, (4) is a third resistor for input, (5) is the input terminal (6)
And (7) a first input signal source, (8) an external temporary grounding capacitor connected to the input terminal (7), and (9) and (10) power supply terminals (11). And fourth and fifth resistors connected between the input terminal (7) and the input terminal (7) and the ground, respectively, to determine an input bias;
A second amplifier circuit having the same open-loop gain as the amplifier circuit (1); and (13) and (14) for negative feedback having the same resistance as the first and second resistors (2) and (3), respectively. The sixth and seventh resistors, (15) an eighth input resistor having the same resistance value as the third resistor (4), and (16) an input terminal (7)
And (17) a second input signal source, (18) a third amplifier circuit having the same open loop gain as the first and second amplifier circuits (1) and (12), (19) and (20) ninth and tenth resistors for negative feedback having the same resistance as the first and second resistors (2) and (3) and the sixth and seventh resistors (13) and (14), respectively. (35) an input eleventh resistor having the same resistance as the third resistor (4) and the eighth resistor (15);
(21) (22) and (23) are bonding pads connected to the respective outputs of the first, second and third amplifier circuits (1) (12) and (18), respectively (24) (25) And (26) are lead terminals connected to bonding pads (21), (22) and (23) by bonding wires (27), (28) and (29), respectively, and (30) and (31) are lead terminals (24). ) And (2
5) and a load such as a headphone connected between the lead terminals (25) and (26). The fourth and fifth resistors (9) and (9) are connected so that the input side of the third amplifier circuit (18) applies the same input DC bias voltage as the first amplifier circuit (1) and the second amplifier circuit (12). It is connected to the connection point A of (10).

According to the circuit of FIG. 2, the lead terminals (24) and (25)
In addition, the DC output voltages of the lead terminals (25) and (26) are equal, the DC current flowing through the loads (30) and (31) disappears, and since there is no coupling capacitor, an amplified signal is output regardless of the frequency. , Broadband amplification.

(C) Problems to be Solved by the Invention However, the integrated circuit as shown in FIG. 2 has a disadvantage that crosstalk between the right channel and the left channel deteriorates. The cause is that the internal resistance and the bonding resistance of the bonding wire (28) between the bonding pad (22) and the lead terminal (25) are included in the output impedance of the third amplifier circuit (18).

 This will be described below.

A schematic diagram of the circuit shown in FIG. 2 is shown in FIG. In FIG. 3, first, second and third amplifier circuits (1) (12)
And the output impedance of (18) are r ₀₁ , r ₀₂ ,
And r ₀₃ , the internal resistances of the bonding wires (27), (28) and (29) are r _W1 , r _W2 and r _W3, and the impedances of the loads (30) and (31) are R _L1 and And R _L2
And

Therefore, considering the case where the first input signal source (5) signal only is applied, when the signal voltage output to the lead terminal (24) from the first amplifier circuit (1) is V _01, the signal cross-talk voltage V ₀₃ generated in the lead terminal (25) by the voltage V ₀₁ is, Becomes

The ratio CT of the signal voltage V ₀₁ and the crosstalk voltage V ₀₃ is From the equations (1) and (2), Becomes Output impedance r of the third amplifier circuit (18)
₀₃ and the internal resistance r _W3 of the bonding wire (28)
0) Since the impedance is smaller than the impedance R _L1 , R _L1 >> r
When _W3 + r _03, (3) formula, Becomes

Accordingly, the crosstalk-signal ratio CT is determined by the internal resistance r _W3 of the output impedance r ₀₃ and bonding wire of the third amplifying circuit (18) (28). That is, the crosstalk becomes worse as the internal resistance r _W3 of the bonding wire (28) increases.

For example, if r _W3 = 200 mΩ and r ₀₃ = 200 mΩ R _L1 = 16Ω, the CT becomes as low as 32 dB. Output impedance
Even if r ₀₃ is substantially “0”, CTmax is only 36 dB. Of course, if the bonding wire (28) is made thicker and shorter, the CT becomes larger, but there is a limit in terms of assembly of an integrated circuit and cost.

(D) Means for Solving the Problems The present invention has been created in view of the above points,
An input DC bias common to the first amplifier circuit, the second amplifier circuit, and the first and second amplifier circuits, and a third amplifier having the same amplification and input impedance and having an output impedance lower than the load impedance. An integrated circuit having an amplifier circuit, wherein a first bonding pad connected to an output of the third amplifier circuit;
A second bonding pad connected to one end of a feedback resistor for feeding back an output signal to an input of the amplifier circuit; an output lead terminal for extracting an output of the third amplifier circuit to the outside; and the first bonding pad And wire bonding between the output lead terminal and the second bonding pad to prevent crosstalk from being deteriorated due to the internal resistance of the bonding wire.

(E) Operation According to the present invention, the internal resistance of the bonding wire connecting the first bonding pad connected to the output of the third amplifier circuit and the output lead terminal is the bonding resistance connecting the output lead terminal and the second bonding pad. Since the wire is connected in series with the feedback resistor and incorporated in the feedback loop, the output impedance as viewed from the output lead terminal including the internal resistance of the bonding wire is reduced, and crosstalk is improved.

(F) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention. In FIG. 1, the same parts as those in the circuit shown in FIG.

The feature of the present invention is that the outputs of the first amplifier circuit (1) and the second amplifier circuit (12) are common to the bonding pads (21) and (23) together with the feedback resistors (2) and (13). While connected, the output of the third amplifier circuit (18) is independently connected to the bonding pad (22), and one end of the feedback resistor (19) is independently connected to the bonding pad (32). That is the point. Then, the output of the third amplifier circuit (18) is taken out, and the lead terminals (25) to which the loads (30) and (31) such as headphones are connected in common and the respective bonding pads (22) and (32) are connected. The spaces are connected by bonding wires (33) and (34). According to the above-described embodiment, the negative feedback loop of the third amplifier circuit (18) includes the bonding pad (22) to the bonding wire (33), the lead terminal (25), the bonding wire (34), the bonding pad (32) and Feedback resistor (1
9) is configured. Therefore, the bonding wire (3
3) Because the internal resistance r _{W3 of the above} is taken into the feedback loop,
The output impedance of the third amplifier circuit (18) as viewed from the lead terminal (25) is reduced.

 Hereinafter, the reason will be described.

First, assuming that the output impedance of the third amplifier circuit (18) itself when no negative feedback is applied to the third amplifier circuit (18) is Z ₀ ′, a feedback resistor (19) is directly connected to the output as shown in FIG. Output impedance Z ₀ Becomes NF is a feedback amount determined by the resistors (19) and (20). Therefore, in the case of FIG. 2, the lead terminal (25)
The output impedance seen from Becomes

On the other hand, when the internal resistance r _W3 of the bonding wire (33) is included in the feedback loop as in this embodiment, the output impedance viewed from the lead terminal (25) is Becomes

Therefore, when Z ₀ ′ = 20Ω, r _W3 = 200 mΩ, and NF = 40 dB, the output impedance Z _{0A in} FIG. In the case of this embodiment, And the value can almost ignore the magnitude of r _W3 .

(G) Effect of the Invention As described above, according to the present invention, the bonding pads for output of the third amplifier circuit and the bonding for feedback to the third amplifier circuit are related to the lead terminals to which the load is commonly connected. By providing the pad independently, and by including the internal resistance of the bonding wire in the feedback loop, there is an advantage that the occurrence of crosstalk can be reduced and the performance and characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a conventional example, and FIG. 3 is a schematic diagram of the circuit diagram of FIG. (1)... First amplifier circuit, (2) (3) (4) (9)
(10) (13) (14) (15) (19) (20) (35) ... resistance, (5) ... first input signal source, (6) (7) (17) ...
... input terminal, (8) ... capacitor, (11) ... power supply terminal, (12) ... second amplifier circuit, (16) ... second input signal source, (18) ... third amplifier circuit, (21) (22) (23) (3
2) Bonding pads (24) (25) (26)
Lead terminals, (27) (28) (29) (33) (34) ... bonding wires.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H03F 3/68

Claims (2)

(57) [Claims] 1. A first amplifier circuit for amplifying a first input signal, a second amplifier circuit for amplifying a second input signal, and an input DC bias common to the first and second amplifier circuits, and the same. An integrated circuit comprising: a third amplifier circuit having an amplification degree and an input impedance and having an output impedance lower than a load impedance, wherein: a first bonding pad connected to an output of the third amplifier circuit; A second bonding pad to which one end of a feedback resistor for feeding back an output signal to an input of the third amplifier circuit is connected, and an output lead terminal of the third amplifier circuit and the first bonding pad are connected by a wire. An integrated circuit, wherein the bonding is performed and the output lead terminal and the second bonding pad are wire-bonded. 2. The integrated circuit according to claim 1, wherein said first bonding pad and said second bonding pad are provided near or adjacent to each other.