CN217159654U - Transimpedance amplifier circuit - Google Patents

Abstract

The utility model discloses a transimpedance amplifier circuit, include: input PAD, first ESD protection device and amplifier circuit, input PAD passes through the bonding wire and connects photodiode, still includes: the input PAD is connected with a primary coil of the T-coil; the first ESD protection device is connected with a center tap of the T-coil; the input end of the amplifying circuit is connected with the secondary coil of the T-coil; and two ends of the T-coil are connected with the bridging capacitor. The utility model provides the high TIA bandwidth to the whole bandwidth of TIA has been reduced the sensitivity to the parasitic inductance of bonding wire.

Description

Transimpedance amplifier circuit

Technical Field

The utility model relates to a transimpedance amplifier.

Background

A Photodiode (PD) and a Trans-impedance amplifier (TIA) are essential modules in an optical communication system, the PD realizes a function of converting an optical signal into a photocurrent, and the TIA realizes a function of converting the photocurrent signal into an electrical signal.

With the increase of the optical communication speed requirement, the parasitic capacitance of the TIA input end becomes one of the important reasons for the bandwidth limitation of the TIA. In order to solve the influence of the stray capacitance of the TIA input end on the bandwidth, in the prior art, there are methods for compensating the bandwidth loss caused by the TIA input capacitance by using the binding Wire inductance of the TIA input end, and there are methods for compensating the bandwidth loss caused by the TIA input capacitance by using methods such as serially connecting the inductance at the TIA input end, and the like.

In an optical communication application environment, the TIA is generally connected to the PD through a Bonding Wire (bond Wire), as shown in fig. 1, and as a schematic diagram of the most common TIA design, an amplifier a and a feedback resistor Rf form an active amplification circuit part of the TIA. The positive end and the negative end of the photodiode are connected with the TIA through the binding Wire (parasitic inductance introduced by the binding Wire at the positive end and the negative end is equivalent to Lponding). Cpd is the parasitic capacitance of the photodiode, Cdacp is a decoupling capacitance added in the TIA chip, and the negative end of the photodiode is in alternating current short circuit with GND (ground end) of the chip.

Cpad is a parasitic capacitance of an input PAD (PAD is a chip and an external environment interface) of the TIA, Cesd is an equivalent parasitic capacitance of an ESD (electrostatic discharge) protection device at the input end of the TIA, Cin is a parasitic capacitance at the input end of the TIA circuit, and the three parallel parasitic capacitances and Lsponding form LC peak ((the LC network generates a passive network peak gain at a higher frequency point) so that the bandwidth of the TIA is expanded.

However, for a high-speed TIA, the parasitic inductance caused by the Bonding Wire will have a huge influence on the TIA bandwidth. However, different application environments correspond to different binding Wire parasitic inductances, and the actual processing precision of the binding Wire also causes the binding Wire inductances to have deviations. Therefore, how to reduce the sensitivity of the TIA bandwidth to the Bonding Wire inductance when the TIA bandwidth is improved has very important significance.

SUMMERY OF THE UTILITY MODEL

An object of the utility model is to provide a transimpedance amplifier circuit improves the TIA bandwidth to the sensitivity of the whole bandwidth of TIA to binding Wire parasitic inductance has been reduced.

The technical scheme for realizing the purpose is as follows:

a transimpedance amplifier circuit comprising: input PAD, first ESD protection device and amplifier circuit, input PAD passes through the bonding wire and connects photodiode, still includes: a T-coil and a bridge capacitor,

the input PAD is connected with the primary coil of the T-coil;

the first ESD protection device is connected with a center tap of the T-coil;

the input end of the amplifying circuit is connected with the secondary coil of the T-coil;

and two ends of the T-coil are connected with the bridging capacitor.

Preferably, the amplifying circuit comprises an amplifier and a feedback resistor connected to two ends of the amplifier, and an input end of the amplifier is connected to the secondary coil of the T-coil.

Preferably, the method further comprises the following steps: a decoupling capacitor;

the anode of the photodiode is connected with an input PAD through a bonding wire, and the cathode of the photodiode is connected with a decoupling capacitor through the bonding wire and then connected with the ground end of the trans-impedance amplifier circuit from the decoupling capacitor.

Preferably, the method further comprises the following steps: a second ESD protection device connected to the primary or secondary coil of the T-coil.

The utility model has the advantages that: the utility model discloses a TIA input series connection T-coil will input PAD, ESD protection device, amplifier and connect respectively at the different nodes of T-coil, has solved the problem that TIA input parasitic capacitance leads to the loss of bandwidth, has solved the problem of the sensitivity of TIA bandwidth along with binding Wire parasitic inductance change simultaneously.

Drawings

FIG. 1 is a circuit diagram of a prior art transimpedance amplifier circuit;

fig. 2 is a circuit diagram of the transimpedance amplifier circuit of the present invention.

Detailed Description

The present invention will be further explained with reference to the accompanying drawings.

Referring to fig. 2, the transimpedance amplifier circuit of the present invention includes: input PAD, first ESD protection device, amplification circuit, T-coil, and bridge capacitor Cb.

The input PAD is connected with the anode of the photodiode PD through a bonding wire, and the cathode of the photodiode PD is connected with a decoupling capacitor Cdecp through the bonding wire and then connected with the ground end of the transimpedance amplifier circuit through the decoupling capacitor.

Primary coil L1 with input PAD connected to T-coil; the first ESD protection device is connected to the center tap of the T-coil (the junction where L1 and L2 are connected). The input of the amplifier circuit is connected to the secondary coil L2 of the T-coil. The amplifier circuit comprises an amplifier A and a feedback resistor Rf connected to both ends of the amplifier A, and the input end of the amplifier A is connected to the secondary coil L2 of the T-coil. The bridge capacitor Cb is connected to both ends of the T-coil. Providing a design freedom for high frequency gain adjustment of the passive network. The high-order passive network is formed by a parasitic capacitor Cpad of an input PAD, an equivalent parasitic capacitor Cesd of a first ESD protection device, a parasitic capacitor Cin of an input end of a TIA circuit (namely, an input end of an amplifying circuit), a parasitic inductor Lbonding introduced by a bonding wire and T-coil.

The T-coil can provide higher passive network gain to further improve the TIA bandwidth, and compared with the first-order LC passive network in the figure 1, the higher-order passive network in the figure 2 has lower Q value (quality factor), so that the gain change at the high frequency of the passive network is smoother, and the gain flatness in the TIA bandwidth range is improved. Meanwhile, the requirement on Lbinding value accuracy in the passive network is lowered by the high-order passive network, and the sensitivity of the whole TIA bandwidth to Lbinding is lowered.

In fig. 2, a parasitic capacitance Cpad of an input PAD, an equivalent parasitic capacitance Cesd of a first ESD protection device, a parasitic capacitance Cin of a TIA circuit input end, and a coupling coefficient k between two coils of a parasitic inductance Lbonding and a T-coil introduced by a bonding wire have a relatively high design freedom, different passive network gain curves can be generated by different value-taking designs, different active circuit amplifier gain curves can be adapted, the overall TIA bandwidth is improved, and the gain flatness of the TIA is optimized. For example, in the figure, the effective parasitic capacitance Cesd is related to the size of the ESD protection device, and the ESD protection device can be separated to be connected at the left end of L1 or the right end of L2, which is equivalent to the Cesd reduction in fig. 2 and the Cpad and Cin increase. Namely: the utility model discloses still include the second ESD protection device, the primary coil L1 or the secondary coil L2 of T-coil are connected to the second ESD protection device. The coupling coefficient k can be 0, and the T-coil is degraded into two independent inductors; the value of the bridging capacitor Cb may be large, a coupling path from the left end of the primary coil L1 to the right end of the secondary coil L2 is formed at a high frequency, and the value of the bridging capacitor Cb may also be zero, which is equivalent to the case of no bridging capacitor.

The above embodiments are provided only for the purpose of illustration, not for the limitation of the present invention, and those skilled in the relevant art can make various changes or modifications without departing from the spirit of the present invention, therefore, all equivalent technical solutions should also belong to the scope of the present invention, and should be defined by the claims.

Claims (4)

1. A transimpedance amplifier circuit comprising: input PAD, first ESD protection device and amplifier circuit, input PAD passes through the bonding wire and connects photodiode, its characterized in that still includes: a T-coil and a bridge capacitor,

the input PAD is connected with the primary coil of the T-coil;

the first ESD protection device is connected with a center tap of the T-coil;

the input end of the amplifying circuit is connected with the secondary coil of the T-coil;

and two ends of the T-coil are connected with the bridging capacitor.

2. The transimpedance amplifier circuit according to claim 1, wherein said amplification circuit comprises an amplifier and a feedback resistor connected across said amplifier, said amplifier having an input connected to said secondary winding of said T-coil.

3. The transimpedance amplifier circuit according to claim 1, further comprising: a decoupling capacitor;

the anode of the photodiode is connected with an input PAD through a bonding wire, and the cathode of the photodiode is connected with a decoupling capacitor through the bonding wire and then connected with the ground end of the trans-impedance amplifier circuit from the decoupling capacitor.

4. The transimpedance amplifier circuit according to claim 1, further comprising: a second ESD protection device connected to the primary or secondary coil of the T-coil.

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