diff --git a/utilities/at32f421_freertos_demo/src/TaskLoop.c b/utilities/at32f421_freertos_demo/src/TaskLoop.c
index eb05e51..aea83cb 100644
--- a/utilities/at32f421_freertos_demo/src/TaskLoop.c
+++ b/utilities/at32f421_freertos_demo/src/TaskLoop.c
@@ -654,25 +654,31 @@ void vd1_task(void)
      *================================================================*/
 
     /* 1a. 慢速 IIR — 斜率限幅 */
-    if (loop1_CAPVD == 0) {
-        loop1_CAPVD = loop1_Value;
-        loop1_CAPVD_fast = loop1_Value;
-    } else {
-        /* 斜率限幅: 物理车辆不可能让频率瞬间跳变 > MAX_SLOPE_RATE% */
-        int32_t raw_delta = (int32_t)loop1_Value - (int32_t)loop1_CAPVD;
-        int32_t max_step = (int32_t)(loop1_CAPVD * MAX_SLOPE_RATE / 100);
-        if (max_step < 100) max_step = 100;  // 最小限幅，防止 origin 很小时锁死
-        if (raw_delta > max_step)  raw_delta = max_step;
-        if (raw_delta < -max_step) raw_delta = -max_step;
-        uint32_t clamped_value = (uint32_t)((int32_t)loop1_CAPVD + raw_delta);
-        loop1_CAPVD = get_flt_value(clamped_value, loop1_CAPVD);
-    }
+    {
+        uint32_t fast_input;  // 快速 IIR 的输入：限幅后的原始值，不经慢速 IIR 滞后
 
-    /* 1b. 快速 IIR — α=0.5: (old + new) / 2 */
-    if (loop1_CAPVD_fast == 0) {
-        loop1_CAPVD_fast = loop1_CAPVD;  // 首次直接锁定
-    } else {
-        loop1_CAPVD_fast = (loop1_CAPVD_fast + loop1_CAPVD) / 2;
+        if (loop1_CAPVD == 0) {
+            loop1_CAPVD = loop1_Value;
+            fast_input = loop1_Value;
+        } else {
+            /* 斜率限幅: 物理车辆不可能让频率瞬间跳变 > MAX_SLOPE_RATE% */
+            int32_t raw_delta = (int32_t)loop1_Value - (int32_t)loop1_CAPVD;
+            int32_t max_step = (int32_t)(loop1_CAPVD * MAX_SLOPE_RATE / 100);
+            if (max_step < 100) max_step = 100;  // 最小限幅，防止 origin 很小时锁死
+            if (raw_delta > max_step)  raw_delta = max_step;
+            if (raw_delta < -max_step) raw_delta = -max_step;
+            uint32_t clamped_value = (uint32_t)((int32_t)loop1_CAPVD + raw_delta);
+            loop1_CAPVD = get_flt_value(clamped_value, loop1_CAPVD);
+            fast_input = clamped_value;
+        }
+
+        /* 1b. 快速 IIR — α=0.5: (old + new) / 2
+         * 输入直接用限幅后的原始值，不经过慢速 IIR，保持 τ≈28ms 的响应速度 */
+        if (loop1_CAPVD_fast == 0) {
+            loop1_CAPVD_fast = fast_input;
+        } else {
+            loop1_CAPVD_fast = (loop1_CAPVD_fast + fast_input) / 2;
+        }
     }
 
     /*--- 2. 稳定期：只跟踪基线，不检测车辆 ---*/