We‘d like use resistor networks and operational amplifiers to monitor the voltage state over telephone lines.（ Please see below）
The voltage on the telephone line, Vtip-ring, is generated by a voltage generator. The Vtip-ring usually has the following values
1.Vtip-ring =0V Indicates that there is no electricity
- Vtip-ring= +10Vdc or -10VDC Indicates that the phone is hang off
- Vtip-ring=+48Vdc or -48 VDC indicates that the phone is hung on
- Vtip-ring= +120V or -120V Indicates that the phone is ringing.
In schematic , measuring vTIP-Ring at high resistance values through resistance networks R1, R2 and R3, and then convert it to voltage values through operational amplifiers . Low accuracy can meet the requirements of distinguishing the above four telephone line states.
The voltage on the phone line, vtip-ring, is usually dc and ac (50Hz Sine wave) when ringing.
My question is
- Can you recommend a single-ended rail-to-rail operational amplifier to meet the needs?
- The voltage generator is connected to a different ground than the operational amplifier.The power supply of the op amp is 5V.In this application, do we need to consider the common mode voltage range of the op amp?
- Sometimes Vtip is greater than Vring (Vtip-ring>0, such as +48V), sometimes Vtip is less than Vring (vtip-ringn>0, such as -48V), how can Vcc/2 be used as the middle voltage in the single-end output of op-amp and be judged as if the value is less than Vcc/2 ,it can be judged as Vtip-ringn<0;
If the value is greater than Vcc/2, it can be judged as Vtip-ring>0?