在设计测试设备时，通常会遇到一套测试设备需测试多个不同点的同类物理量。通常的做法是信号调理及ADC部分共用，采样则是多通道分时采样，这就涉及到采样切换开关，最常用与最方便的就是模拟开关，模拟开关的英文名为Analog Switch，它可以通过逻辑信号方便实现模拟信号切换。说起模拟开关，我们可能很容易想到CD4051，CD4052，CD4053等，是不是所有模拟开关都可以用于测试采样？答案是否定的。特别是对于被测信号为小的微弱直流信号时，如果用于多通道选择采样的模拟开关选择不当的话，根本检测不到被测信号，如果你对模拟开关不是很熟悉，此时，你最好干脆采用信号继电器来做多通道选择采样，不然你可能会面临意想不到的困难。但是，用信号继电器，又会面临切换速度慢的问题。信号继电器要完成通道切换，直到信号稳定，一般耗时不会小于25毫秒。下面介绍几款用于多通道选择采样的模拟开关。

1. DG406 DG406是16选一模拟开关，它具有漏流小、导通阻抗小等特点可用于多通道采样。

下面是MAXIM DG406的介绍：

The DG406 is a 1 of 16 multiplexer/demultiplexer，operate with a +4.5V to +30V single
supply and with ±4.5V to ±20V dual supplies. ESD pro-tection is guaranteed to be greater than 2000V perMethod 3015.7 of MIL-STD 883.

Guaranteed Matching Between Channels, 8Ω Max.

Guaranteed On-Resistance Flatness, 9Ω Max

Guaranteed Low Charge Injection, 15pC Max

 Low On-Resistance 100Ω Max

 Input Leakage, 5nA Max at +85°C

Low Power Consumption, 1.25mW Max

Rail-to-Rail Signal Handling

Digital Input Controls TTL/CMOS Compatible

ESD Protection >2000V per Method 3015.7

Applications

Sample-and-Hold Circuits
Test Equipment
Guidance and Control Systems
Communications Systems
Data-Acquisition Systems
Audio Signal Routing

Pin脚定义如下：

 真值表如下：

 有多家厂商生产DG406，Pin脚定义及真值表完全相同，但电气参数不尽相同。如VISHAY的DG406，其导通电阻大概是MAXIM的一半（50Ω Max）。

2. DG407  DG407的电气特性与DG406一致。不同的是，DG407是一个8选一差分模拟开关，可用来切换差分模拟信号， DG407的Pin脚定义如下：

 DG407的真值表如下：

 3. DG408/DG409 DG408是一款8选一的模拟开关，DG409是一款4选一的差分模拟开关。下面是Intersil的DG408/DG409介绍：

The DG408 Single 8-Channel, and DG409 Differential 4-Channel monolithic CMOS analog multiplexers are drop-in replacements for the popular DG508A and DG509A series
devices. They each include an array of eight analog switches, a TTL/CMOS compatible digital decode circuit for channel selection, a voltage reference for logic thresholds and an ENABLE input for device selection when several multiplexers are present.

Features
• ON Resistance (Max, 25 o C). . . . . . . . . . . . . . . . . . . 100Ω
• Low Power Consumption (P D ) . . . . . . . . . . . . . . . <11mW
• Fast Switching Action
- t TRANS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .<250ns
- t ON/OFF(EN) . . . . . . . . . . . . . . . . . . . . . . . . . . . .<150ns
• Low Charge Injection
• Upgrade from DG508A/DG509A
• TTL, CMOS Compatible
• Single or Split Supply Operation
Applications
• Data Acquisition Systems
• Audio Switching Systems
• Automatic Testers
• Hi-Rel Systems
• Sample and Hold Circuits
• Communication Systems
• Analog Selector Switch

DG408的Pin脚定义如下：

 DG409的Pin脚定义如下：

DG408的真值表如下：

 DG409的真值表如下：

 4. ADG706/ADG707   ADG706是一款16选一模拟开关，ADG707是一款8选一差分模拟开关。ADG706/ADG707的Pin脚定义与DG406/DG407一致，但是封装存在差异，可能没法直接替代。

ADG706/ADG707的Pin脚定义如下：

 ADG706/ADG707的真值表如下：

 个人觉得ADG706/ADG707更适合于多通道采样，下面是ADG706/ADG707的部分特点描述。

FEATURES
+1.8 V to +5.5 V Single Supply
+/-2.5 V Dual Supply
2.5 Ω ON Resistance
0.5 Ω ON Resistance Flatness
100 pA Leakage Currents
40 ns Switching Times
Single 16-to-1 Multiplexer ADG706
Differential 8-to-1 Multiplexer ADG707
28-Lead TSSOP Package
Low-Power Consumption
TTL/CMOS-Compatible Inputs
APPLICATIONS
Data Acquisition Systems
Communication Systems
Relay Replacement
Audio and Video Switching
Battery-Powered Systems

5. ADG408/ADG409 ADG408是一款8选一的模拟开关，ADG409是一款4选一模拟开关。下面是ADG408/ADG409的部分特点描述：

FEATURES
44 V Supply Maximum Ratings
V SS to V DD Analog Signal Range
Low On Resistance (100 V max)
Low Power (I SUPPLY < 75 mA)
Fast Switching
Break-Before-Make Switching Action
Plug-in Replacement for DG408/DG409
APPLICATIONS
Audio and Video Routing
Automatic Test Equipment
Data Acquisition Systems
Battery Powered Systems
Sample and Hold Systems
Communication Systems

PRODUCT HIGHLIGHTS
1. Extended Signal Range
The ADG408/ADG409 are fabricated on an enhanced
LC 2 MOS process giving an increased signal range that
extends to the supply rails.
2. Low Power Dissipation
3 Low R ON
4. Single Supply Operation
For applications where the analog signal is unipolar, the
ADG408/ADG409 can be operated from a single rail power
supply. The parts are fully specified with a single +12 V
power supply and will remain functional with single supplies
as low as +5 V.

DG408/DG409的Pin脚定义与DG408/DG409的Pin脚一致。DG408/DG409的Pin脚定义如下：

DG408/DG409的真值表如下：

 6. SGM84782  SGM4782是一款4选一差分模拟开关，是一款本土企业产品。其部分特点描述如下：

The SGM84782 is high-speed, low-voltage, low
on-resistance, CMOS analog multiplexer/switch that
configured as two 4-channel multiplexers. It operates
from a single +1.8V to +4.2V power supply. Targeted
applications include battery powered equipment that
benefit from low R ON (4Ω) and fast switching speeds
(t ON = 17ns, t OFF = 9ns).
The SGM84782 can handle rail-to-rail analog signals
and is available in Green TQFN-3×3-16L and
TSSOP-16 packages.
APPLICATIONS
Communication Systems
Cell Phones
Portable Instrumentation
Audio Signal Routing
Audio and Video Switching
Computer Peripherals
Low-Voltage Data-Acquisition Systems

FEATURES
  Voltage Operation: 1.8V to 4.2V
  Low On-Resistance: 4Ω (TYP) at 4.2V
  Low On-Resistance Flatness
  -3dB Bandwidth: 150MHz
  Fast Switching Times (+4.2V)
t ON 17ns
t OFF 9ns
  Low Crosstalk: -92dB at 10MHz
  Rail-to-Rail Input and Output Operation
  Typical Power Consumption (< 0.01μW)
  TTL/CMOS Compatible
  Break-Before-Make Switching
  -40 ℃ to +85 ℃ Operating Temperature Range
  Available in Green TQFN-3×3-16L and TSSOP-16
Package

SGM84782的Pin脚定义如下：

SGM84782的真值表如下：

CD74HC4067

CD74HC4067 作用是选通一路对十六路模拟信号，更详细的说，根据芯片上 S0-S3 四个不同管脚的组合，让SIG管脚和C0-C15导通。因此，最常见的用法是用来测试模拟信号。比如，Arduino Uno上面只有6个模拟输入，用一个CD74HC4067可以多扩展出来16个，于是可以支持 6+16-1=21个模拟引脚。
一开始原理图上没注意使能引脚接地的，默认是使能状态，换句话说，EN使能引脚是可以通过电平控制的(后面在做项目的时候由于默认低电平使能吃亏了)后面我会在具体说。(高电平断开 低电平使能)

STM32控制原理和代码

一开始默认使能状态，就直接通过S0-S3引脚的组合来控制C0-C15(16个通道的导通就可以了)

具体的代码思路就是把四个使能的引脚写到一个数组当中，然后用一个二维数组模拟出16个通道的情况，在用循环把4个通道的情况写入。不多说，具体看代码。

// 写入到函数当中，方便MAIN中调用
void readMux1(int channel)
{
	int controlpin[4]={GPIO_PIN_12,GPIO_PIN_13,GPIO_PIN_14,GPIO_PIN_15}; //这里我使用的是PB12-PB14
	int i;
	int muxChannel[16][4]=
	{

    {0,0,0,0}, //channel 0

    {1,0,0,0}, //channel 1

    {0,1,0,0}, //channel 2

    {1,1,0,0}, //channel 3

    {0,0,1,0}, //channel 4

    {1,0,1,0}, //channel 5

    {0,1,1,0}, //channel 6

    {1,1,1,0}, //channel 7

    {0,0,0,1}, //channel 8

    {1,0,0,1}, //channel 9

    {0,1,0,1}, //channel 10

    {1,1,0,1}, //channel 11

    {0,0,1,1}, //channel 12

    {1,0,1,1}, //channel 13

    {0,1,1,1}, //channel 14

    {1,1,1,1}  //channel 15

  };
	
	for(i = 0; i < 4; i ++)
	{
	   HAL_GPIO_WritePin(GPIOB,controlpin[i],muxChannel[channel][i]);
	
	}
}

// MAIN函数的调用
int main()
{
		 for(j = 0; j < 16; j++)
		{
			  readMux(j); //调用需要配置的通道
            HAL_Delay(1);  //这里配置完一个通道需要进行延迟，不然通道会出现问题
        }
        return 0;
}

出现的问题以及解决方法

因为项目的需要，需要两个模拟开关对32个通道进行循环开启，所以直接就把两个模拟开关打在同一个板子上面，并且两个使能引脚同时接地，以为没有问题，结果程序写好之后，发现两个芯片会产生干扰，一个模拟开关的通道会影响另一个模拟开关的所有通道。最后找了半天问题发现两个开关不能同时使能工作。解决方法就是把两个开关的使能引脚接入MCU，通过MCU来进行使能。
解决了两个通道相互影响的问题。大概代码如下。

	PB11_ENABLE;  
    PB10_DISABLE;//防止对另一个通道造成影响
    HAL_Delay(1); //突变的原因是因为使能之后不能立刻读取数据，需要延迟一下
   	for(k=0;k<16;k++)
   	{
   	    readMux1(k);  //控制通断
        HAL_Delay(1);
    }
   PB10_ENABLE;
   PB11_DISABLE;
   HAL_Delay(1);
		
  for(j = 0; j < 16; j++)
	{
        readMux1(j);  //控制通断
        HAL_Delay(1);
    }

第一次写博客，简单的记录一下。工程都是HAL库配置的
参考链接：http://www.lab-z.com/cd74hc4067/