Description

The AN22023A-VT is an amplifier circuit designed to be a simple and low-cost add-on to the SA253x single chip telephone family. It amplifies the receive signal from the RO1 or RO2 outputs of the telephone. Although it does not have advanced features such as channel switching or anti-larsen circuit, it can enable full duplex "handsfree" operation at short distances (<2m) when the handset is placed next to the telephone with the microphone facing the user. The SA253x circuits have excellent sidetone cancellation, which prevents howling between the handset microphone and loudspeaker in normal operation.

Specifications and features

• Low-cost additional circuit for loudhearing function
• Full duplex "handsfree" operation with handset microphone and loudspeaker (at distances <2m)
• Compatible with any SA253x application
• Enables use of low-cost 8Ω loudspeaker
• High output power with low distortion
• Powered entirely from the telephone line
• No influence on loudspeaker amplifier in AC-impedance, sidetone cancellation, or DC-mask
• Loudspeaker volume adjustable by potentiometer

Application Scenarios

The AN22023A-VT amplifier circuit can be used in a variety of scenarios, including:

• Improving the volume and sound quality of telephones
• Adding loudhearing function to telephones

Comparison

- Low-cost solution

- Enables full duplex "handsfree" operation

- Can be added to any SA253x application

- High output power with low distortion

- Easy installation as it is powered from the telephone line

- Sidetone cancellation prevents howling between microphone and loudspeaker

- No advanced features such as channel switching or anti-larsen circuit

- Lower receive and transmit gains to avoid howling

- Limited to short distances (<2m) for full duplex operation