LM565 is a general-purpose PLL (Phase phase-locked loop) IC designed for demodulation, frequency multiplication and frequency division. The device mainly consists of two components, one is voltage controller oscillator and other is phase detector. In which VCO is designed for highly linear operation and PD with good carrier suppression.
Pin Configuration
LM565 is a 14 pin device and the function of each pin is stated below.
| Pin | Name | Function |
| 1 | -Vcc | Negative power supply input pin |
| 2 | Input | Phase detector input pin (FM signal input) |
| 3 | Input | Phase detector input pin (FM signal input) |
| 4 | VCO output | VCO (Voltage Control Oscillator) output seen at this pin |
| 5 | Phase comparator VCO input | Phase detector input pin (VCO output is feedback through this pin) |
| 6 | Reference output | Internal amplifier reference output |
| 7 | VCO control voltage | VCO control voltage can be seen at this pin |
| 8 | Timing Resistor | Resistor to free running frequency of VCO |
| 9 | Timing Capacitor | Capacitor for free running frequency of VCO |
| 10 | +Vcc | Positive power supply |
| 11 | NC | No connection |
| 12 | NC | No connection |
| 13 | NC | No connection |
| 14 | NC | No connection |
LM565 Features and Characteristics
- Wide power supply range
- 0.2% linearity of demodulated output
- Linear triangle wave with in-phase zero crossings available
- TTL and DTL compatible phase detector input and square wave output
- Adjustable hold in range from ±1% to > ±60%
- 200 ppm/°C frequency stability of the VCO
- VCO maximum operating frequency: 500KHz
- Operating voltage range: ±5V to ±12V
- Maximum operating voltage: ±12V
- Operating temperature range: -55ºC to +125ºC
- Storage Temperature Range: -65°C to +150°C
- Power supply current: 12.5mA
- Maximum power dissipation: 1400mW
LM565 IC Overview
LM565 is basically used in applications where a PLL is required, such as FM demodulation and Signal frequency divider or multiplier. The device has specifically designed highly linear VCO for the low distortion FM demodulation. The device being cheap can be used in applications where cost is considered.
How to use LM565 IC in a Circuit
First let us consider the internal block diagram of the LM565 PLL chip.
In order to understand let us simplify this block diagram further to get the following.
In the device pin 2 and pin3 are inputs where we can connect the input analog signal but usually pin 3 will be grounded and pin2 is used as input.
The input signal goes in to the phase detector along with VCO feedback and this phase detector compares whether both signal are in same phase (or frequency).If they are in phase (or frequency) the PD provides zero voltage output and if phase (or frequency) is present the PD provides positive output voltage.
This output voltage of PD is given to amplifier to amplify the voltage signal and the amplified voltage is given to VCO, which generates waveform whose frequency depends on magnitude of the given input voltage.
Now consider no input is given, under such case the VCO will be in free running mode generating signal whose frequency is determined by the capacitor and resistor connected at the pin 8 and pin 9.
When a signal is given at the input, the frequency of both input signal and the VCO output is compared. And if they are not a match the PD will provide a voltage which is amplified and fed to VCO. The VCO will increase or decrease the signal frequency depending of the fed voltage of amplifier. Once the adjustment is done both the input signal frequency and VCO frequency will match.
This is how a phase locked loop works, the VCO output signal frequency will always tries to keep up with the input signal frequency.
Applications
- FSK and FM demodulation
- Data and tape synchronization
- Modems
- Frequency synthesizer
- Tone decoding
- Frequency multiplication and division
- SCA demodulators
- Telemetry receivers
- Signal regeneration
- Coherent demodulators
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