STM32L1 Discovery Kit 5MHz PWM Generation

Question

I have been using the STM32L1 Discovery Kit with the STM32L152RCT6 MCU.

A project that I am working on requires me to output two PWM signals. One of these is a 100KHz square wave and the other is 5MHz square wave.

I have gotten the 100KHz wave to work correctly, however I am unable to generate a 5MHz pwm from my board. I am using Timers 4 and 11 currently to generate these two signals and the code is as follows:

/* TIM3 init function */
static void MX_TIM3_Init(void)
{
    TIM_ClockConfigTypeDef sClockSourceConfig;
    TIM_MasterConfigTypeDef sMasterConfig;
    TIM_OC_InitTypeDef sConfigOC;
    htim3.Instance = TIM3;
    htim3.Init.Prescaler = 2;
    htim3.Init.CounterMode = TIM_COUNTERMODE_UP;
    htim3.Init.Period = 2;
    htim3.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
    if (HAL_TIM_Base_Init(&htim3) != HAL_OK)
    {
        _Error_Handler(__FILE__, __LINE__);
    }
    sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
    if (HAL_TIM_ConfigClockSource(&htim3, &sClockSourceConfig) != HAL_OK)
    {
        _Error_Handler(__FILE__, __LINE__);
    }
    if (HAL_TIM_PWM_Init(&htim3) != HAL_OK)
    {
        _Error_Handler(__FILE__, __LINE__);
    }
    sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
    sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
    if (HAL_TIMEx_MasterConfigSynchronization(&htim3, &sMasterConfig) != HAL_OK)
    {
        _Error_Handler(__FILE__, __LINE__);
    }
    sConfigOC.OCMode = TIM_OCMODE_PWM1;
    sConfigOC.Pulse = 1;
    sConfigOC.OCPolarity = TIM_OCPOLARITY_HIGH;
    sConfigOC.OCFastMode = TIM_OCFAST_DISABLE;
    if (HAL_TIM_PWM_ConfigChannel(&htim3, &sConfigOC, TIM_CHANNEL_1) != HAL_OK)
    {
        _Error_Handler(__FILE__, __LINE__);
    }
    HAL_TIM_MspPostInit(&htim3);
}

/* TIM4 init function */
static void MX_TIM4_Init(void)
{
    TIM_ClockConfigTypeDef sClockSourceConfig;
    TIM_MasterConfigTypeDef sMasterConfig;
    TIM_OC_InitTypeDef sConfigOC;
    htim4.Instance = TIM4;
    htim4.Init.Prescaler = 106;
    htim4.Init.CounterMode = TIM_COUNTERMODE_UP;
    htim4.Init.Period = 2;
    htim4.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
    if (HAL_TIM_Base_Init(&htim4) != HAL_OK)
    {
        _Error_Handler(__FILE__, __LINE__);
    }
    sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
    if (HAL_TIM_ConfigClockSource(&htim4, &sClockSourceConfig) != HAL_OK)
    {
        _Error_Handler(__FILE__, __LINE__);
    }
    if (HAL_TIM_PWM_Init(&htim4) != HAL_OK)
    {
        _Error_Handler(__FILE__, __LINE__);
    }
    sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
    sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
    if (HAL_TIMEx_MasterConfigSynchronization(&htim4, &sMasterConfig) != HAL_OK)
    {
        _Error_Handler(__FILE__, __LINE__);
    }
    sConfigOC.OCMode = TIM_OCMODE_PWM1;
    sConfigOC.Pulse = 1;
    sConfigOC.OCPolarity = TIM_OCPOLARITY_HIGH;
    sConfigOC.OCFastMode = TIM_OCFAST_DISABLE;
    if (HAL_TIM_PWM_ConfigChannel(&htim4, &sConfigOC, TIM_CHANNEL_1) != HAL_OK)
    {
        _Error_Handler(__FILE__, __LINE__);
    }
    HAL_TIM_MspPostInit(&htim4);
}

/* TIM11 init function */
static void MX_TIM11_Init(void)
{
    TIM_ClockConfigTypeDef sClockSourceConfig;
    TIM_OC_InitTypeDef sConfigOC;
    htim11.Instance = TIM11;
    htim11.Init.Prescaler = 2;
    htim11.Init.CounterMode = TIM_COUNTERMODE_UP;
    htim11.Init.Period = 2;
    htim11.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
    if (HAL_TIM_Base_Init(&htim11) != HAL_OK)
    {
        _Error_Handler(__FILE__, __LINE__);
    }
    sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
    if (HAL_TIM_ConfigClockSource(&htim11, &sClockSourceConfig) != HAL_OK)
    {
        _Error_Handler(__FILE__, __LINE__);
    }
    if (HAL_TIM_PWM_Init(&htim11) != HAL_OK)
    {
        _Error_Handler(__FILE__, __LINE__);
    }
    sConfigOC.OCMode = TIM_OCMODE_PWM1;
    sConfigOC.Pulse = 1;
    sConfigOC.OCPolarity = TIM_OCPOLARITY_HIGH;
    sConfigOC.OCFastMode = TIM_OCFAST_DISABLE;
    if (HAL_TIM_PWM_ConfigChannel(&htim11, &sConfigOC, TIM_CHANNEL_1) != HAL_OK)
    {
        _Error_Handler(__FILE__, __LINE__);
    }
    HAL_TIM_MspPostInit(&htim11);
}

When I run my board with this code I find that the TIM4 correctly ouputs a 100KHz square wave with a peak to peak voltage of 3V. The TIM11 channel outputs an unclean square wave with a very low peak to peak voltage and only approx. a 3.5MHz signal. If I try to reduce the prescaler value to 1 in order to increase the frequency further, I lose the waveform completely. The results from the oscilliscope are show below:

TIM4 -

TIM11 -

The more I increase the prescaler value on the TIM11 channel the cleaner the wave becomes and the peak to peak voltage increases until it reaches 3V with a prescaler of approx. 10 to 15.

Any help on getting the TIM11 pwm to be a clean square at 5MHz with 3V peak to peak would be greatly appreciated.

Thank you!

UPDATE 1

The high setting did work!

I now am getting the 5.3MHz wave. however I am also getting a significant amount of noise on both timer channels now: Zooming in closer:

UPDATE 2

I believe I can filter remaining noise with an RC filter but should anyone know of a way of doing this on the MCU that would be great!