diff --git a/.github/workflows/CI-models.yml b/.github/workflows/CI-models.yml
index cc7b41b9..2883600b 100644
--- a/.github/workflows/CI-models.yml
+++ b/.github/workflows/CI-models.yml
@@ -32,7 +32,6 @@ jobs:
           python-version: ${{ matrix.python-version }}
       - name: Install dependencies
         run: |
-          pip install taichi-nightly -i https://pypi.taichi.graphics/simple/
           if [ -f requirements-dev.txt ]; then pip install -r requirements-dev.txt; fi
           pip uninstall brainpy -y
           python setup.py install
@@ -80,7 +79,6 @@ jobs:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies
       run: |
-        pip install taichi-nightly -i https://pypi.taichi.graphics/simple/
         if [ -f requirements-dev.txt ]; then pip install -r requirements-dev.txt; fi
         pip uninstall brainpy -y
         python setup.py install
@@ -130,7 +128,6 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install numpy>=1.21.0
-        pip install taichi-nightly -i https://pypi.taichi.graphics/simple/
         python -m pip install -r requirements-dev.txt
         python -m pip install tqdm brainpylib
         pip uninstall brainpy -y
diff --git a/brainpy/_src/dnn/activations.py b/brainpy/_src/dnn/activations.py
index 1073c7ec..84b7e400 100644
--- a/brainpy/_src/dnn/activations.py
+++ b/brainpy/_src/dnn/activations.py
@@ -840,10 +840,10 @@ class Softplus(Layer):
       >>> output = m(input)
   """
   __constants__ = ['beta', 'threshold']
-  beta: int
-  threshold: int
+  beta: float
+  threshold: float
 
-  def __init__(self, beta: int = 1, threshold: int = 20) -> None:
+  def __init__(self, beta: float = 1, threshold: float = 20.) -> None:
     super().__init__()
     self.beta = beta
     self.threshold = threshold
diff --git a/brainpy/_src/dyn/synapses/abstract_models.py b/brainpy/_src/dyn/synapses/abstract_models.py
index 2125da34..4864b8d6 100644
--- a/brainpy/_src/dyn/synapses/abstract_models.py
+++ b/brainpy/_src/dyn/synapses/abstract_models.py
@@ -262,6 +262,7 @@ def update(self):
   Args:
     tau_decay: float, ArrayArray, Callable. The time constant of the synaptic decay phase. [ms]
     tau_rise: float, ArrayArray, Callable. The time constant of the synaptic rise phase. [ms]
+    normalize: bool. Normalize the raise and decay time constants so that the maximum conductance is 1. Default False.
     %s
   """
 
@@ -277,6 +278,7 @@ def __init__(
       # synapse parameters
       tau_decay: Union[float, ArrayType, Callable] = 10.0,
       tau_rise: Union[float, ArrayType, Callable] = 1.,
+      normalize: bool = False,
   ):
     super().__init__(name=name,
                      mode=mode,
@@ -285,8 +287,15 @@ def __init__(
                      sharding=sharding)
 
     # parameters
+    self.normalize = normalize
     self.tau_rise = self.init_param(tau_rise)
     self.tau_decay = self.init_param(tau_decay)
+    if normalize:
+      self.a = ((1 / self.tau_rise - 1 / self.tau_decay) /
+                (self.tau_decay / self.tau_rise * (bm.exp(-self.tau_rise / (self.tau_decay - self.tau_rise)) -
+                                                   bm.exp(-self.tau_decay / (self.tau_decay - self.tau_rise)))))
+    else:
+      self.a = 1.
 
     # integrator
     self.integral = odeint(JointEq(self.dg, self.dh), method=method)
@@ -306,7 +315,7 @@ def dg(self, g, t, h):
   def update(self, x):
     # update synaptic variables
     self.g.value, self.h.value = self.integral(self.g.value, self.h.value, share['t'], dt=share['dt'])
-    self.h += x
+    self.h += self.a * x
     return self.g.value
 
   def return_info(self):
@@ -422,6 +431,7 @@ def __init__(self, pre, post, delay, prob, g_max, tau_decay, tau_rise, E):
   Args:
     tau_decay: float, ArrayArray, Callable. The time constant of the synaptic decay phase. [ms]
     tau_rise: float, ArrayArray, Callable. The time constant of the synaptic rise phase. [ms]
+    normalize: bool. Normalize the raise and decay time constants so that the maximum conductance is 1. Default True.
     %s
   """
 
@@ -437,6 +447,7 @@ def __init__(
       # synapse parameters
       tau_decay: Union[float, ArrayType, Callable] = 10.0,
       tau_rise: Union[float, ArrayType, Callable] = 1.,
+      normalize: bool = True,
   ):
     super().__init__(name=name,
                      mode=mode,
@@ -445,9 +456,13 @@ def __init__(
                      sharding=sharding)
 
     # parameters
+    self.normalize = normalize
     self.tau_rise = self.init_param(tau_rise)
     self.tau_decay = self.init_param(tau_decay)
-    self.coeff = self.tau_rise * self.tau_decay / (self.tau_decay - self.tau_rise)
+    if normalize:
+      self.a = self.tau_rise * self.tau_decay / (self.tau_decay - self.tau_rise)
+    else:
+      self.a = 1.
 
     # integrator
     self.integral = odeint(lambda g, t, tau: -g / tau, method=method)
@@ -463,7 +478,7 @@ def update(self, x=None):
     self.g_decay.value = self.integral(self.g_decay.value, share['t'], self.tau_decay, share['dt'])
     if x is not None:
       self.add_current(x)
-    return self.coeff * (self.g_decay - self.g_rise)
+    return self.a * (self.g_decay - self.g_rise)
 
   def add_current(self, inp):
     self.g_rise += inp
@@ -471,7 +486,7 @@ def add_current(self, inp):
 
   def return_info(self):
     return ReturnInfo(self.varshape, self.sharding, self.mode,
-                      lambda shape: self.coeff * (self.g_decay - self.g_rise))
+                      lambda shape: self.a * (self.g_decay - self.g_rise))
 
 
 DualExponV2.__doc__ = DualExponV2.__doc__ % (pneu_doc,)
diff --git a/brainpy/_src/math/activations.py b/brainpy/_src/math/activations.py
index 60c7991f..54ced5d4 100644
--- a/brainpy/_src/math/activations.py
+++ b/brainpy/_src/math/activations.py
@@ -298,7 +298,7 @@ def leaky_relu(x, negative_slope=1e-2):
   return jnp.where(x >= 0, x, negative_slope * x)
 
 
-def softplus(x, beta=1, threshold=20):
+def softplus(x, beta: float = 1., threshold: float = 20.):
   r"""Softplus activation function.
 
   Computes the element-wise function
@@ -315,12 +315,12 @@ def softplus(x, beta=1, threshold=20):
   Parameters
   ----------
   x: The input array.
-  beta: the :math:`\beta` value for the Softplus formulation. Default: 1
-  threshold: values above this revert to a linear function. Default: 20
+  beta: the :math:`\beta` value for the Softplus formulation. Default: 1.
+  threshold: values above this revert to a linear function. Default: 20.
 
   """
   x = x.value if isinstance(x, Array) else x
-  return jnp.where(x > threshold, x * beta, 1 / beta * jnp.logaddexp(beta * x, 0))
+  return jnp.where(x > threshold / beta, x, 1 / beta * jnp.logaddexp(beta * x, 0))
 
 
 def log_sigmoid(x):
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 51f41a41..0e475e83 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -7,7 +7,7 @@ matplotlib
 msgpack
 tqdm
 pathos
-taichi
+taichi==1.7.0
 
 # test requirements
 pytest
diff --git a/requirements-doc.txt b/requirements-doc.txt
index 6e9f851e..8b0a5a6a 100644
--- a/requirements-doc.txt
+++ b/requirements-doc.txt
@@ -5,7 +5,7 @@ matplotlib
 numpy
 scipy
 numba
-taichi
+taichi==1.7.0
 
 # document requirements
 pandoc