FDC2112: some questions about the resonant wave

Eric Liu(SZ-FAE)

Part Number: FDC2112

1、Does the chip require oscillating waveforms as shown in the figure below?

2, how does the internal core calculate the frequency of Fin, and is the number of pulses calculated by a fixed time? How does the counter convert a sine wave to a square wave?

2 年多前

0 Amy Luo 2 年多前

TI__Guru**** 185470 points

Hi Eric,

1. Yes.

2. The core uses a reference frequency (fREF) to measure the sensor frequency. fREF is derived from either an internal reference clock (oscillator), or an externally supplied clock. The digitized output for each channel is proportional to the ratio of fSENSOR/fREF.

The FDC estimates the LC resonant frequency by counting the LC waveform's axis crossings over a time interval described in equation (5) in the data sheet:
t_cx = (CHx_RCOUNT x 16 + 4)/f_REFx

where CHx_RCOUNT is the number of reference clock cycles used to measure the sensor frequency for that channel, and f_REFx is the reference clock frequency.

For the FDC2112, the output data is related to the LC sensor resonant frequency via equation (1) in the data sheet.

DATAx = f_SENSORx x 2¹²/f_REFx

0 Eric Liu(SZ-FAE) 2 年多前回复 Amy Luo

TI__Prodigy 45 points

Amy 您好，我直接中文吧，我想确认两个问题，1、第一个内部core计算振荡频率是通过比较参考时钟和外部lc振荡波形在一固定窗口时间的波形重复计数吗？

2、如果我是用差分输入模式，而两个输入端的正负半周波形不对称，如上图所示，影响FDC2112的输出结果吗？

0 Amy Luo 2 年多前回复 Eric Liu(SZ-FAE)

TI__Guru**** 185470 points

1、是通过计算RCOUNT设置的时间间隔或者说窗口时间内多个传感器信号周期内的参考时钟周期数来估计传感器信号频率。

2、看上述波形幅值不满足规格范围：1.2V~1.8V，建议您参照datasheet 第10部分的设计步骤调节 IDRIVE值。

我不确定是否会影响FDC的输出，但是您可以根据输出DATAx和示波器测量的传感器f_SENSORx频率根据下面公式来验证输出是否正常

DATAx = f_SENSORx x 2¹²/f_REFx

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FDC2112: some questions about the resonant wave