Digital Position Sensor ICs—Continuous-Time to Chopper-Stabilized Cross-Reference Guide

Digital Position Sensor ICs—Continuous-Time to Chopper-Stabilized Cross-Reference Guide

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Joseph Hollins，
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Introduction

Allegro提供各种数字位置传感器，包括霍尔效应开关，闩锁和其他特殊用途。随着时间的推移和随着创新，这些霍尔效应传感器的基本架构已经从原始形式（连续时间）进入当今现代，斩波稳定的设备。

此应用程序指南将概述两个传感器类型之间的差异，并为系统设计人员提供所需的工具，以便为其系统选择合适的传感器。还提供了一种交叉参考表，其总结了在从连续时间设备升级到斩波器稳定设备时要使用的建议的替换装置。

斩波稳定的与连续时间 - 有什么区别？

In general, chopper-stabilized devices offer superior temperature stability and stress-resistance (lower switch point drift) and a streamlined production flow versus continuous-time devices. They may also have the advantage of small die size due to the lack of trimming and the use of a more modern wafer fabrication processes. There is a small trade-off in time-domain performance, but this is negligible in most applications. Table 1 summarizes the differences between typical Allegro devices of each type.

All of Allegro’s newest sensor products are chopper-stabilized, and chopper-stabilized devices are recommended for all designs. The slightly faster response time and incrementally lower-jitter of continuous-time devices are insignificant in typical applications. Continuous-time devices remain in production but are only recommended for special applications with extremely fast-moving targets, or those planning to rapidly power-cycle the sensor for ultra-low power consumption (maximum battery life), or to minimize self-heating. The differences in time-domain behavior are quantified below.

Even in these special situations, the time-domain performance of continuous-time devices may not outweigh the advantages of chopper-stabilized devices in a given application.

Table 1: Chopper-Stabilized versus Continuous-Time Sensors

Parameter	Chopper-Stabilized	Continuous-Time
Range of magnetic switch-points?	Yes	Yes
典型包装	SOT23（LH），SIP-3（UA），SIP-3带有无线（UC）	SOT23 (LH), SIP-3 (UA)
信号路径	More complex	Less complex
Hall-plate configuration	Single, dual, or more	Single
哈尔板偏见	Switched (“chopped”)	Constant
Trimming required in Allegro production?	No	Yes
BOP/RPTemperature Stability	Best	Good
Stress Resistance	Best	Good
Power-On Time	Fast	Fastest
Maximum operating frequency	High	Highest
Output Repeatability/Jitter	Good	Good
fCoscillator?	Yes	No
典型的C.BYPASS*	0.1 μF	0.01 μF
推荐所有应用程序？亚博尊贵会员	Yes / All	Special situations only

* Refer to the device datasheet for specific recommendations and guidelines.

Continuous-Time

Sensors employing continuous-time operation use only one direction of current flow across the Hall element, and this bias current is constant. This allows the fastest response time between the applied external magnetic field and the electrical output. It is clear how this might be beneficial for applications requiring the fastest output response time.

磁性偏移随环境条件而变化，会影响霍尔开关阈值的稳定性（操作和释放阈值，B_OPand B_RP, respectively). In continuous-time devices, there is no built-in circuitry to remove offsets. This is reflected in the specifications given in the device datasheet: the specified B_OPand B_RPranges for a continuous-time device are wider than for a comparable chopper-stabilized device.

Chopper Stabilization

When using Hall-effect technology, a limiting factor for switch point accuracy is the small signal voltage developed across the Hall element(s). This signal voltage is disproportionally small relative to the offsets that can be produced at the output of the Hall element(s). This makes it difficult to accurately process the magnetic signal over the specified operating temperature and voltage ranges.

斩波稳定用于最小化霍尔元素中的偏移。专利的Allegro技术，动态正交偏移消除（U.S.专利No.5621319,1997，现在已过期），除去热量和机械应力引起的输出偏移和漂移的关键源。该偏移稳定技术基于信号调制/解调过程。不希望的偏移信号通过调制与频域中的磁场感应信号分离。随后的磁信号解调作为偏移的调制，使得磁场感应的信号在基带处恢复其原始频谱，而DC偏移变为高频信号。然后，磁信号可以通过低通滤波器，而调制的DC偏移被抑制。该信号链配置如图3所示。当信号链可能看起来比连续时间设备的相比看起来更复杂，缺少装饰控制块，因为不需要。这导致芯片区域节省和生产校准时间。图4示出了交替的霍尔元素偏置，导致取消偏移。

In most instances, Allegro’s chopper stabilization employs an 800 kHz clock. For the demodulation process, a sample-and-hold technique is used where the sampling is performed at twice the chopper frequency. This high-frequency operation allows a higher overall sampling rate.

Dynamic Quadrature Offset Cancellation desensitizes the chip to the effects of thermal and mechanical stress and results in extremely stable quiescent Hall output voltages and precise recovery after temperature cycling. Allegro implements this technique in proprietary BiCMOS wafer fabrication processes that support the use of low-offset, low-noise amplifiers in combination with high-density logic and sample-and-hold circuits.

输出的响应时间（传播延迟）和时域重复性（抖动）略微受到斩波稳定的影响。然而，Allegro高频斩波方法最小化这些效果，在大多数应用中使它们难以察觉。亚博尊贵会员在大厅中连续切换偏置电流
element(s) creates brief, periodic interruptions in the bias current. These perturbations may be observable at the device’s supply pin, resulting in a larger recommended bypass capacitor.

Performance

The performance data (Table 2) is for example purposes only and was collected using two Allegro digital position sensor ICs, namely the A1220 (chopper-stabilized) and the A1201 (continuous- time).

POWER-ON TIME

数字位置传感器的上电时间通过测量达到最小指定工作电压和输出处于有效状态的电源之间的时间延迟。响应外部字段生成输出边缘，B = B_RP(MIN)– 10 G is applied. (Typically, applying a
larger field will cause the observed power-on time to decrease.)

The shorter power-on time of continuous-time devices can be advantageous in applications that rapidly power-cycle the sensor for ultralow power consumption (maximum battery life) or to minimize self-heating. The total time during which the sensor must be powered to produce a valid output is less, resulting in
a lower duty cycle, lower average power consumption, and less self-heating.

OUTPUT RESPONSE TIME

The response time is measured from the magnetic signal edge to the output edge. The applied magnetic field will propagate through the simpler continuous-time signal path more quickly than the chopper-stabilized device. However, the chopper-stabilized device still responds within 12 μs (See Figure 6).

Output response time can become important for applications which operate at very high frequencies. The maximum operating frequency supported is directly related to the output response time, in addition to the signal path bandwidth.

Continuous-time devices typically respond to the magnetic field within 2 μs, enabling operation up to a theoretical 250 kHz (calculated using two output transitions per period). Chopper-stabilized devices have typical response times of 11.4 μs and theoretically support operation up to nearly 44 kHz. While this is a 6:1 advantage for the continuous-time device, the absolute delay times are extremely small in both cases and are not a factor in most practical applications. For both device types, the actual maximum operating frequency is limited by the bandwidth of the signal path.

An important relationship exists between ring magnet pole-pair count, target rotation speed, and device operating frequency, f. This relationship is depicted in Figure 7 and expressed in the formula below:

In this expression, the target velocity, RPM, and the target polepair count, P_P, determine the effective operating frequency of the Hall-effect sensor.

抖动

相对于一致磁输入信号的传感器输出的可重复性（抖动）由信噪比和刷新率（如果斩波稳定）确定。连续时间设备产生恒定的霍尔信号，延迟非常可忽略。斩波稳定的装置需要两个或更多个霍尔信号样本在输出可以刷新之前进行。这可以根据磁信号转换相对于斩波稳定相的定时何时贡献输出信号中的抖动。

For example, a device with an 800 kHz chopping frequency and 4× chopping (driving current from each of the four corners of the Hall element) will refresh the output state at a rate of:

Figure 7 includes several examples of ring magnet pole-pair counts and the resultant magnetic pole-pair frequency. As shown, a high density ring magnet will produce an increased operating frequency for a given target speed. However, all are well within the frequencies which can be measured with Allegro Hall technology.

This 200 kHz rate is equal to a refresh every 5 μs, which, when added to the delay contributed by the remainder of the signal path, can result in a total propagation delay of 6 to 12 μs for a typical chopper-stabilized device.

下面的重复性与温度比较（见图9）表明，两个传感器类型实际上都表现出类似的性能。所示的数据是典型的6-Sigma边缘可重复性，其使用直径为100mm的60杆环环磁体。显示在X轴上的BPKPK表示磁场输入的幅度。图8包含用于量化可重复性的测量方法的示例。当这种方式测量重复性时，较小的值表示更好的性能，即少抖动。图10说明了可重复性与目标速度的变化非常稳定。

Temperature has the greatest influence on repeatability. Other contributors include magnetic field strength and consistency as well as target speed. However, the rising and falling edge repeatability for slow speeds is only marginally better than when operating at higher speeds for both the continuous-time and the chopper-stabilized devices.

温度稳定性

Chopper-stabilized devices provide an advantage in temperature stability over continuous-time devices. When sensing some magnetic materials, such as ferrite, a drift in magnetic field strength over temperature will occur. Unless one is trying to track the significant temperature drift of a given target, it is ideal for the magnetic switching thresholds to remain constant and within the expected magnetic field input range, for all temperatures.

Better temperature stability is achieved with chopper-stabilized devices. Switch threshold variations are minimized due to the averaging and offset cancellation taking place during chopper stabilization. The data in the adjacent plots (Figure 11 and Figure 12) summarize the standard deviation of the magnetic switch threshold parameters from their typical values for a continuous-time and chopper-stabilized device.

In this example, the standard deviation of the continuous-time devices is typically 3× larger than for the chopper-stabilized devices.

Continuous-time devices are significantly affected by increased temperature, and as a result, the switch threshold variation is up to 5× larger than its chopper-stabilized counterpart. This can result in degraded edge location (timing) accuracy and may require higher magnetic fields from the target and/or a smaller air
gap.

示例标准磁交换机阈值参数的偏差数据如下所示（表4）。不同的工作电压对标准偏差具有可忽略的影响。

Table 4: Standard Deviation Switch Threshold Data

Datasheet Parameter	设置	Magnetic Threshold Parameter Standard Deviation, σ (G)
		TA = –40°C		TA = 25°C		TA = 150°C
		Chopper- 稳定	Continuous- Time	Chopper- 稳定	Continuous- Time	Chopper- 稳定	Continuous- Time
Operate Point, BOP	VCC = 3 V	2.24	7.33	2.23	6.01	2.78	12.03
	VCC = 24 V	2.19	7.28	2.24	6.00	2.78	12.12
Release Point, BRP	VCC = 3 V	2.23	6.97	2.12	5.67	2.52	12.88
	VCC = 24 V	2.29	6.97	2.09	5.61	2.45	13.07
Hysteresis, BHYS	VCC = 3 V	1.89	2.83	2.61	2.36	1.87	2.59
	VCC = 24 V	1.87	2.72	2.64	2.44	1.72	2.68

Cross-Reference Table

Chopper-stabilized devices are recommended for all applications. The table below should be used as a guide to determine the most suitable chopper-stabilized replacement for a given continuous time device.

Table 5: Continuous-Time to Chopper-Stabilized Cross-Reference

	Device Type	Part Number	BOP (max)	BRP（分钟）	BHYS	Chopper-Stabilized Replacement
	Unipolar Switches	A1101	175	10	80	A1121
		A1102	245	60.	80	A1122
		A1103	35.5	150.	80	A1123
		A1104	450	35.	80	A1121 or A1128
		A1106	430	160.	140.	A1123 or A1128
	Bipolar Switches	A1201	50.	-50	55.	APS12200 or A1250
		A1202	75	-75	150.	APS12200 or APS12210
		A1203	95	-95年	190	APS12210
		A1205	50.	-50	55.	APS12200 or A1250
	Latches	A1210	150.	-150	300	A1222
		A1211	180	-180	360	APS12230
		A1212	175	-175	35.0	APS12230
		A1213	200	-200	400	APS12230
		A1214	300	-300	60.0	APS12230

Summary

Chopper-stabilized设备进攻r many improvements over continuous-time products. In general, chopper-stabilized devices offer superior temperature stability and stress-resistance (lower switch point drift) and a streamlined production flow versus continuous-time devices. They typically also have the advantage of smaller die size due to the lack of trimming and the use of more modern wafer fabrication processes. There is a small tradeoff in time-domain performance, but this is negligible in most applications.

所有chopper-stabi快板的最新产品lized, and chopper-stabilized devices are recommended for all new applications. The slightly faster power-on and incrementally shorter output-delay time of continuous-time devices are generally insignificant. Continuous-time devices remain in production, but are only recommended for special applications, e.g.,

• Applications where the sensor is power-managed by switching its power supply on and off, as continuous-time devices have faster power-on times.
• Extremely high-speed applications that demand the highest operating frequency and absolute lowest jitter/best repeatability, as there is no multiphase chopping action causing additional delay or jitter.

If your applications falls into one of these categories, please consult with your local Allegro field applications engineer to confirm if a continuous-time device is the best choice for your design.