Zhongke Lanxun's interface circuit design scheme realizes chip voltage compatibility and multi-output

Recently, according to relevant information on the Shanghai Stock Exchange website, Shenzhen Zhongke Bluexun Co., Ltd. (hereinafter referred to as "Zhongke Bluexun") announced the first round of inquiry responses for the Science and Technology Innovation Board IPO. It is mainly engaged in the production of wireless audio SoC chips, which can be used in TWS Bluetooth headsets and other devices.

We know that when a chip exchanges data with an external device, an interface circuit is usually required, and multiple interface circuits may also need to be set up. A typical interface circuit consists of a buffer stage and a driver stage, as shown in the following figure:

The buffer stage is responsible for receiving logic signals, performing level conversion, and generating non-overlapping signals. The driver stage is responsible for outputting high and low levels, driving off-chip loads, and also has ESD protection functions. By controlling the input signal, "1" or "0" can be obtained on the output pin.

In some specific cases, the interface circuit sometimes needs to output different voltages. For example, when two voltages need to be output, each interface circuit can be provided with driver stage 1 and driver stage 2. Driver stage 1 requires a first power supply voltage, and driver stage 2 requires a second power supply voltage. The corresponding driver stage is enabled according to the input signal and the selection signal, and different voltages are output on the output pin.

Therefore, in the existing solutions, an ESD protection circuit usually needs to be designed on each power supply group, which undoubtedly occupies more chip area and chip IO position and leads to an increase in chip cost.

To this end, Zhongke Bluexun applied for an invention patent named "Interface Circuit and Chip" (application number: 202110358655.6) on April 2, 2021. The applicant is Shenzhen Zhongke Bluexun Technology Co., Ltd. In this patent, a chip technology was invented that only needs one set of power supply voltages to achieve multi-voltage output.

Based on the relevant information currently disclosed by the patent, let us take a look at this solution.

As shown in the figure above, it is a schematic diagram of the multi-voltage interface output circuit invented in the patent, and the interface circuit 500 includes a buffer stage 50, a first driver stage 51, a second driver stage 52 and a level control module 53. The buffer stage is composed of a series of buffers and other components, which are used to realize the level conversion of the received logic signal and the generation of non-overlapping signals.

It can receive control signals from processors and other similar functional modules, and the control signals include selection signals and input signals. The buffer stage can select to enable the first driver stage or the second driver stage according to the selection signal, and output a corresponding voltage signal on the interface pin 50a according to the input signal, thereby obtaining pulse signals of different amplitudes.

The first driver stage and the second driver stage are driver circuit modules used to drive the interface pins to the corresponding voltages. Two MOS tubes are used to form the driver stage in the figure above. When the interface circuit is in different output states, different driver stages will be started: in the first output state, the first driver stage is enabled, so that the interface pin outputs the first voltage; in the second output state, the second driver stage is enabled, so that the interface pin outputs the second voltage.

The level control module is connected to the second driver stage and the interface pin respectively. In the second output state, the level control module detects the voltage of the interface pin, and when the voltage of the interface pin is increased to the second voltage, controls the second driver stage to stop increasing the voltage of the interface pin.

As shown in the figure above, it is a circuit schematic diagram of this level control module. The detection unit mainly includes a first MOS tube MN1, a second MOS tube MP1 and a load resistor R1, wherein the source of the first MOS tube MN1 is connected to the interface pin, and its gate is coupled to the reference voltage. The reference voltage is a preset voltage value used to provide a reference standard. When the voltage of the interface pin of the first MOS tube MN1 reaches the second voltage, the operating state will be switched.

The gate of the second MOS transistor MP1 is used to receive an input signal, and its drain is connected to the drain of the first MOS transistor MN1. One end of the load resistor R1 is coupled to the power supply, and the other end is respectively connected to the gate of the P-type MOS transistor of the second driving stage and the source of the second MOS transistor MP1 to control the voltage value of the interface pin.

The above is the relevant technical solution of the interface circuit in the chip invented by Zhongke Bluexun. In this solution, only one set of power supply voltage is needed to achieve multi-voltage output. Therefore, under the premise of effectively reducing the circuit design area, it not only reduces the use of electronic components, but also supports the output of multiple pulse signals, so as to effectively control various types of external devices.