数字位置传感器IC连续时间斩波稳定的交叉参考指南

数字位置传感器IC连续时间斩波稳定的交叉参考指南

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B.y Joseph Hollins,
一种llegro MicroSystems, LLC

Introduction

快速的提供了一个广泛的数字位置nsors consisting of Hall-effect switches, latches and other special purpose devices. Over time and with ongoing innovation, the basic architecture of these Hall-effect sensors has evolved from its original form (continuous-time) into today’s modern, chopper-stabilized devices.

This application guide will outline the differences between the two sensor types and provide system designers with the tools needed in order to select the appropriate sensor for their system. A cross-reference table is also provided, which summarizes the suggested replacement device to be used when upgrading from a continuous-time device to a chopper-stabilized device.

Chopper-Stabilized vs. Continuous-Time—What Is the Difference?

通常，斩波稳定装置提供卓越的温度稳定性和应力阻力（下换股点漂移）和流线型生产流量与连续时间装置。由于缺乏修剪和使用更现代的晶片制造工艺，它们也可能具有小模糊尺寸的优点。在时间域的性能下有一个小的权衡，但在大多数应用中，这可以忽略不计。雷竞技最新网址表1总结了每种类型的典型Allegro设备之间的差异。

快板的所有最新的传感器产品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

P.arameter	Chopper-Stabilized	Continuous-Time
Range of magnetic switch-points?	Yes	Yes
Typical packages	年代OT23 (LH), SIP-3 (UA)	年代OT23 (LH), SIP-3 (UA)
年代ignal path	More complex	Less complex
Hall-plate configuration	年代ingle, dual, or more	年代ingle
Hall-plate bias	年代witched (“chopped”)	Constant
Trimming required in Allegro production?	No	Yes
B.OP/RPTemperature Stability	最好	Good
年代tress Resistance	最好	Good
P.ower-On Time	Fast	Fastest
Maximum operating frequency	High	最高
Output Repeatability/Jitter	Good	Good
fCoscillator?	Yes	No
Typical CB.YPASS*	0.1 μF	0.01 μF
Recommended for all applications?	Yes / All	仅限特殊情况

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

Continuous-Time

年代ensors 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.

Magnetic offset changes with environmental conditions and will affect the stability of the Hall switch thresholds (the Operate and Release thresholds, B_OPand B_rp.那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_rp.ranges 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 switchpoint 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.

Chopper stabilization is used to minimize offsets in the Hall element(s). The patented Allegro technique, Dynamic Quadrature Offset Cancellation (U.S. Patent No. 5621319, 1997, now expired), removes key sources of output offset and drift induced by thermal and mechanical stresses. This offset stabilization technique is based on a signal modulation/demodulation process. The undesired offset signal is separated from the magnetic-field-induced signal in the frequency domain through modulation. The subsequent demodulation of the magnetic signal acts as a modulation of the offset, causing the magnetic-field-induced signal to recover its original spectrum at baseband while the DC offset becomes a high-frequency signal. The magnetic signal can then pass through a low-pass filter, while the modulated DC offset is suppressed. This signal chain configuration is illustrated in Figure 3. While the signal chain may look more complex than that of the continuous-time device, the Trim Control block is missing, as it is not needed. This leads to savings in chip area and production calibration time. Figure 4 illustrates the alternating Hall element bias that leads to the cancellation of offsets.

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.

The output’s response time (propagation delay) and time-domain repeatability (jitter) are affected slightly by chopper stabilization. However, the Allegro high-frequency chopping approach minimizes these effects and makes them imperceptible in most applications. Continuously switching the bias current in the Hall
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.

P.erformance

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).

P.OWER-ON TIME

The power-on time of a digital position sensor is characterized by measuring the time delay between the power supply reaching the minimum specified operating voltage and the output being in a valid state. To generate an output edge in response to the external field, 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
较低的占空比，较低的平均功耗，较少的自加热。

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).

输出响应时间对于在非常高的频率下运行的应用可能变得重要。雷竞技最新网址除了信号路径带宽之外，支持的最大工作频率与输出响应时间直接相关。

连续时间设备通常响应2μs内的磁场，使得能够达到理论为250kHz（使用每个时段的两个输出转换计算）。Chopperstableized设备具有11.4μs的典型响应时间，并且理论上支持近44 kHz的操作。虽然这是连续时间设备的6：1优势，但两种情况下绝对延迟时间非常小，并且不是大多数实际应用中的因素。雷竞技最新网址对于两个设备类型，实际最大工作频率受信号路径带宽的限制。

一种n 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.那determine the effective operating frequency of the Hall-effect sensor.

JITTER

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。持续恒星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。

例如，具有800 kHz斩波频率和4×斩波的设备（来自霍尔元素的四个角中的每一个的驱动电流）将以以下速率刷新输出状态：

图7包括环磁极对计数的几个例子和所得磁极对频率。如图所示，高密度环磁体将产生给定目标速度的增加的工作频率。但是，一切都在频率内，可以使用Allegro Hall技术测量。

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.

The repeatability versus temperature comparison below (see Figure 9) shows that both sensor types actually exhibit similar performance. The data shown are typical 6-Sigma edge repeatability results using a 60 pole-pair ring magnet with a diameter of 100 mm. BPkPk, shown on the x-axis, represents the magnitude of the magnetic field input. Figure 8 contains an example of the measurement method used to quantify repeatability. When repeatability is measured this way, smaller values indicate better performance, i.e., less jitter. Figure 10 illustrates that the repeatability is very stable with changes in target speed.

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.

TEMPERATURE STABILITY

斩波稳定装置在连续时间装置上的温度稳定性提供了优势。当感测某些磁性材料（例如铁氧体）时，将发生在温度上的磁场强度的漂移。除非试图跟踪给定目标的显着温度漂移，对于所有温度，否则是磁性开关阈值保持恒定和在预期磁场输入范围内的理想选择。

B.etter 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
间隙。

Example standard deviation data for the magnetic switch threshold parameters are shown below (Table 4). Different operating voltages have a negligible effect on the standard deviation.

Table 4: Standard Deviation Switch Threshold Data

Datasheet P.arameter	年代etup	Magnetic Threshold Parameter Standard Deviation, σ (G)
		TA = –40°C		TA = 25°C		TA = 150°C
		Chopper- 年代tabilized	Continuous- Time	Chopper- 年代tabilized	Continuous- Time	Chopper- 年代tabilized	Continuous- Time
Operate Point, B.OP	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
滞后， B.HYS	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	零件号	B.OP (max)	BRP.(min)	B.HYS	Chopper-Stabilized Replacement
	单极 年代witches	A1101	175	10.	80	一种1121
		A1102	245.	60	80	一种1122
		A1103	355.	150	80	一种1123
		A1104.	450	35	80	一种1128
		A1106	430	160	140	一种1128
	B.ipolar 年代witches	A1201.	50	-50	55	一种1220 or A1250
		A1202.	75	-75	150	A1220或A1221.
		A1203.	95	-95	190	A1221.
		A1205.	50	-50	55	一种1220 or A1250
	Latches	一种1210	150	-150	300	A1222
		一种1211	180	-180	360.	A1223
		一种1212	175	-175	350.	A1223
		一种1213	200	-200	400	A1223
		一种1214	300	-300.	600	A1223

年代ummary

斩波稳定的设备可以通过连续时间产品提供许多改进。通常，斩波稳定装置提供卓越的温度稳定性和应力阻力（下换股点漂移）和流线型生产流量与连续时间装置。由于缺乏修剪和使用更现代的晶片制造工艺，它们通常还具有较小的模具尺寸的优点。在时间域的性能中有一个小的权衡，但在大多数应用中，这可以忽略不计。雷竞技最新网址

一种ll of Allegro’s newest products are chopper-stabilized, 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.,

• 雷竞技最新网址通过打开和关闭传感器的电源来管理传感器的应用，因为连续时间设备具有更快的电源供电。
• 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.